Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $172.56   12.371%   $193.9074   $193.91   $193.90   $193.90  
  Purchase #2 $226.96   9.182%   $247.7995   $247.80   $247.80   $247.80  
  Purchase #3 $178.97   4.125%   $186.3525   $186.35   $186.35   $186.40  
  Purchase #4 $184.77   9.232%   $201.828   $201.83   $201.85   $201.80  
  Purchase #5 $226.85   5.147%   $238.526   $238.53   $238.55   $238.50  
  Purchase #6 $143.33   5.715%   $151.5213   $151.52   $151.50   $151.50  
  Purchase #7 $151.84   13.185%   $171.8601   $171.86   $171.85   $171.90  
  7 purchase totals = $1,285.28       $1,391.7948   $1,391.80   $1,391.80   $1,391.80