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 $226.42   9.445%   $247.8054   $247.81   $247.80   $247.80  
  Purchase #2 $55.34   5.817%   $58.5591   $58.56   $58.55   $58.60  
  Purchase #3 $90.40   6.742%   $96.4948   $96.49   $96.50   $96.50  
  Purchase #4 $31.48   3.658%   $32.6315   $32.63   $32.65   $32.60  
  Purchase #5 $152.38   7.532%   $163.8573   $163.86   $163.85   $163.90  
  Purchase #6 $61.84   11.520%   $68.964   $68.96   $68.95   $69.00  
  Purchase #7 $191.50   6.427%   $203.8077   $203.81   $203.80   $203.80  
  7 purchase totals = $809.36       $872.1198   $872.12   $872.10   $872.20