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 $186.79   8.667%   $202.9791   $202.98   $203.00   $203.00  
  Purchase #2 $161.62   6.279%   $171.7681   $171.77   $171.75   $171.80  
  Purchase #3 $59.36   5.408%   $62.5702   $62.57   $62.55   $62.60  
  Purchase #4 $42.72   6.327%   $45.4229   $45.42   $45.40   $45.40  
  Purchase #5 $153.75   4.800%   $161.13   $161.13   $161.15   $161.10  
  Purchase #6 $140.36   6.563%   $149.5718   $149.57   $149.55   $149.60  
  Purchase #7 $222.86   8.145%   $241.0119   $241.01   $241.00   $241.00  
  7 purchase totals = $967.46       $1,034.4540   $1,034.45   $1,034.40   $1,034.50