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 $95.52   9.820%   $104.9001   $104.90   $104.90   $104.90  
  Purchase #2 $69.96   11.126%   $77.7437   $77.74   $77.75   $77.70  
  Purchase #3 $186.73   9.221%   $203.9484   $203.95   $203.95   $203.90  
  Purchase #4 $236.26   11.557%   $263.5646   $263.56   $263.55   $263.60  
  Purchase #5 $27.55   12.570%   $31.013   $31.01   $31.00   $31.00  
  Purchase #6 $104.94   13.131%   $118.7197   $118.72   $118.70   $118.70  
  Purchase #7 $13.46   6.547%   $14.3412   $14.34   $14.35   $14.30  
  7 purchase totals = $734.42       $814.2307   $814.22   $814.20   $814.10