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 $110.87   6.742%   $118.3449   $118.34   $118.35   $118.30  
  Purchase #2 $175.98   13.594%   $199.9027   $199.90   $199.90   $199.90  
  Purchase #3 $32.36   13.772%   $36.8166   $36.82   $36.80   $36.80  
  Purchase #4 $70.79   3.150%   $73.0199   $73.02   $73.00   $73.00  
  Purchase #5 $162.72   6.266%   $172.916   $172.92   $172.90   $172.90  
  Purchase #6 $163.55   6.701%   $174.5095   $174.51   $174.50   $174.50  
  Purchase #7 $219.78   12.264%   $246.7338   $246.73   $246.75   $246.70  
  7 purchase totals = $936.05       $1,022.2434   $1,022.24   $1,022.20   $1,022.10