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 $248.71   10.863%   $275.7274   $275.73   $275.75   $275.70  
  Purchase #2 $60.32   3.385%   $62.3618   $62.36   $62.35   $62.40  
  Purchase #3 $34.26   5.430%   $36.1203   $36.12   $36.10   $36.10  
  Purchase #4 $128.50   13.359%   $145.6663   $145.67   $145.65   $145.70  
  Purchase #5 $83.44   9.474%   $91.3451   $91.35   $91.35   $91.30  
  Purchase #6 $183.89   10.638%   $203.4522   $203.45   $203.45   $203.50  
  Purchase #7 $232.64   5.198%   $244.7326   $244.73   $244.75   $244.70  
  7 purchase totals = $971.76       $1,059.4057   $1,059.41   $1,059.40   $1,059.40