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 $54.29   13.676%   $61.7147   $61.71   $61.70   $61.70  
  Purchase #2 $94.33   9.426%   $103.2215   $103.22   $103.20   $103.20  
  Purchase #3 $121.70   13.358%   $137.9567   $137.96   $137.95   $138.00  
  Purchase #4 $67.49   8.461%   $73.2003   $73.20   $73.20   $73.20  
  Purchase #5 $228.52   13.777%   $260.0032   $260.00   $260.00   $260.00  
  Purchase #6 $188.65   4.508%   $197.1543   $197.15   $197.15   $197.20  
  Purchase #7 $114.43   11.269%   $127.3251   $127.33   $127.35   $127.30  
  7 purchase totals = $869.41       $960.5758   $960.57   $960.55   $960.60