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 $239.91   11.628%   $267.8067   $267.81   $267.80   $267.80  
  Purchase #2 $157.63   5.543%   $166.3674   $166.37   $166.35   $166.40  
  Purchase #3 $39.53   12.199%   $44.3523   $44.35   $44.35   $44.40  
  Purchase #4 $23.34   9.807%   $25.629   $25.63   $25.65   $25.60  
  Purchase #5 $36.99   12.315%   $41.5453   $41.55   $41.55   $41.50  
  Purchase #6 $237.36   13.330%   $269.0001   $269.00   $269.00   $269.00  
  Purchase #7 $205.99   3.169%   $212.5178   $212.52   $212.50   $212.50  
  7 purchase totals = $940.75       $1,027.2186   $1,027.23   $1,027.20   $1,027.20