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 $207.69   13.425%   $235.5724   $235.57   $235.55   $235.60  
  Purchase #2 $24.29   3.738%   $25.198   $25.20   $25.20   $25.20  
  Purchase #3 $150.90   11.242%   $167.8642   $167.86   $167.85   $167.90  
  Purchase #4 $27.66   13.348%   $31.3521   $31.35   $31.35   $31.40  
  Purchase #5 $64.90   7.623%   $69.8473   $69.85   $69.85   $69.80  
  Purchase #6 $142.42   3.112%   $146.8521   $146.85   $146.85   $146.90  
  Purchase #7 $178.26   12.714%   $200.924   $200.92   $200.90   $200.90  
  7 purchase totals = $796.12       $877.6101   $877.60   $877.55   $877.70