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 $212.52   10.746%   $235.3574   $235.36   $235.35   $235.40  
  Purchase #2 $10.70   11.380%   $11.9177   $11.92   $11.90   $11.90  
  Purchase #3 $119.45   11.158%   $132.7782   $132.78   $132.80   $132.80  
  Purchase #4 $218.76   6.496%   $232.9706   $232.97   $232.95   $233.00  
  Purchase #5 $62.68   5.254%   $65.9732   $65.97   $65.95   $66.00  
  Purchase #6 $40.33   10.558%   $44.588   $44.59   $44.60   $44.60  
  Purchase #7 $48.48   8.464%   $52.5833   $52.58   $52.60   $52.60  
  7 purchase totals = $712.92       $776.1684   $776.17   $776.15   $776.30