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 $54.55   13.537%   $61.9344   $61.93   $61.95   $61.90  
  Purchase #2 $45.45   6.814%   $48.547   $48.55   $48.55   $48.50  
  Purchase #3 $67.55   11.669%   $75.4324   $75.43   $75.45   $75.40  
  Purchase #4 $24.68   4.572%   $25.8084   $25.81   $25.80   $25.80  
  Purchase #5 $82.95   9.299%   $90.6635   $90.66   $90.65   $90.70  
  Purchase #6 $198.93   11.352%   $221.5125   $221.51   $221.50   $221.50  
  Purchase #7 $216.44   12.482%   $243.456   $243.46   $243.45   $243.50  
  7 purchase totals = $690.55       $767.3542   $767.35   $767.35   $767.30