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 $229.94   7.524%   $247.2407   $247.24   $247.25   $247.20  
  Purchase #2 $44.97   4.179%   $46.8493   $46.85   $46.85   $46.80  
  Purchase #3 $54.84   11.109%   $60.9322   $60.93   $60.95   $60.90  
  Purchase #4 $60.67   10.549%   $67.0701   $67.07   $67.05   $67.10  
  Purchase #5 $88.52   11.529%   $98.7255   $98.73   $98.75   $98.70  
  Purchase #6 $205.26   3.574%   $212.596   $212.60   $212.60   $212.60  
  Purchase #7 $74.95   3.765%   $77.7719   $77.77   $77.75   $77.80  
  7 purchase totals = $759.15       $811.1857   $811.19   $811.20   $811.10