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 $37.42   13.162%   $42.3452   $42.35   $42.35   $42.30  
  Purchase #2 $236.55   12.422%   $265.9342   $265.93   $265.95   $265.90  
  Purchase #3 $243.57   4.508%   $254.5501   $254.55   $254.55   $254.60  
  Purchase #4 $36.98   13.151%   $41.8432   $41.84   $41.85   $41.80  
  Purchase #5 $177.52   13.700%   $201.8402   $201.84   $201.85   $201.80  
  Purchase #6 $202.95   4.361%   $211.8006   $211.80   $211.80   $211.80  
  Purchase #7 $167.40   5.345%   $176.3475   $176.35   $176.35   $176.30  
  7 purchase totals = $1,102.39       $1,194.6610   $1,194.66   $1,194.70   $1,194.50