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 $54.49   7.636%   $58.6509   $58.65   $58.65   $58.70  
  Purchase #2 $93.57   9.576%   $102.5303   $102.53   $102.55   $102.50  
  Purchase #3 $105.54   7.116%   $113.0502   $113.05   $113.05   $113.10  
  Purchase #4 $124.98   7.784%   $134.7084   $134.71   $134.70   $134.70  
  Purchase #5 $200.73   3.205%   $207.1634   $207.16   $207.15   $207.20  
  Purchase #6 $57.52   4.501%   $60.109   $60.11   $60.10   $60.10  
  Purchase #7 $143.91   3.537%   $149.0001   $149.00   $149.00   $149.00  
  7 purchase totals = $780.74       $825.2123   $825.21   $825.20   $825.30