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 $69.79   8.553%   $75.7591   $75.76   $75.75   $75.80  
  Purchase #2 $56.35   4.191%   $58.7116   $58.71   $58.70   $58.70  
  Purchase #3 $18.60   10.568%   $20.5656   $20.57   $20.55   $20.60  
  Purchase #4 $24.99   11.740%   $27.9238   $27.92   $27.90   $27.90  
  Purchase #5 $84.40   8.835%   $91.8567   $91.86   $91.85   $91.90  
  Purchase #6 $121.25   11.772%   $135.5236   $135.52   $135.50   $135.50  
  Purchase #7 $180.95   11.474%   $201.7122   $201.71   $201.70   $201.70  
  7 purchase totals = $556.33       $612.0526   $612.05   $611.95   $612.10