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 $181.49   11.102%   $201.639   $201.64   $201.65   $201.60  
  Purchase #2 $53.27   9.538%   $58.3509   $58.35   $58.35   $58.40  
  Purchase #3 $113.66   11.276%   $126.4763   $126.48   $126.50   $126.50  
  Purchase #4 $71.79   11.292%   $79.8965   $79.90   $79.90   $79.90  
  Purchase #5 $163.35   4.185%   $170.1862   $170.19   $170.20   $170.20  
  Purchase #6 $110.26   10.536%   $121.877   $121.88   $121.90   $121.90  
  Purchase #7 $86.59   11.597%   $96.6318   $96.63   $96.65   $96.60  
  7 purchase totals = $780.41       $855.0577   $855.07   $855.15   $855.10