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 $58.55   10.478%   $64.6849   $64.68   $64.70   $64.70  
  Purchase #2 $219.92   9.817%   $241.5095   $241.51   $241.50   $241.50  
  Purchase #3 $119.47   8.811%   $129.9965   $130.00   $130.00   $130.00  
  Purchase #4 $8.43   7.277%   $9.0435   $9.04   $9.05   $9.00  
  Purchase #5 $112.70   8.549%   $122.3347   $122.33   $122.35   $122.30  
  Purchase #6 $61.61   13.223%   $69.7567   $69.76   $69.75   $69.80  
  Purchase #7 $128.61   8.592%   $139.6602   $139.66   $139.65   $139.70  
  7 purchase totals = $709.29       $776.9860   $776.98   $777.00   $777.00