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 $54.48   8.113%   $58.9   $58.90   $58.90   $58.90  
  Purchase #2 $206.26   3.179%   $212.817   $212.82   $212.80   $212.80  
  Purchase #3 $160.84   3.806%   $166.9616   $166.96   $166.95   $167.00  
  Purchase #4 $11.32   6.589%   $12.0659   $12.07   $12.05   $12.10  
  Purchase #5 $86.36   6.590%   $92.0511   $92.05   $92.05   $92.10  
  Purchase #6 $174.79   4.249%   $182.2168   $182.22   $182.20   $182.20  
  Purchase #7 $82.92   10.786%   $91.8638   $91.86   $91.85   $91.90  
  7 purchase totals = $776.97       $816.8762   $816.88   $816.80   $817.00