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 $194.76   3.214%   $201.0196   $201.02   $201.00   $201.00  
  Purchase #2 $164.65   12.173%   $184.6928   $184.69   $184.70   $184.70  
  Purchase #3 $178.99   13.722%   $203.551   $203.55   $203.55   $203.60  
  Purchase #4 $39.73   11.442%   $44.2759   $44.28   $44.30   $44.30  
  Purchase #5 $11.52   10.764%   $12.76   $12.76   $12.75   $12.80  
  Purchase #6 $133.84   12.449%   $150.5017   $150.50   $150.50   $150.50  
  Purchase #7 $28.98   9.836%   $31.8305   $31.83   $31.85   $31.80  
  7 purchase totals = $752.47       $828.6315   $828.63   $828.65   $828.70