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 $55.41   11.863%   $61.9833   $61.98   $62.00   $62.00  
  Purchase #2 $75.61   12.257%   $84.8775   $84.88   $84.90   $84.90  
  Purchase #3 $198.48   12.428%   $223.1471   $223.15   $223.15   $223.10  
  Purchase #4 $115.55   5.251%   $121.6175   $121.62   $121.60   $121.60  
  Purchase #5 $175.75   5.855%   $186.0402   $186.04   $186.05   $186.00  
  Purchase #6 $70.52   13.705%   $80.1848   $80.18   $80.20   $80.20  
  Purchase #7 $64.28   4.672%   $67.2832   $67.28   $67.30   $67.30  
  7 purchase totals = $755.60       $825.1336   $825.13   $825.20   $825.10