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 $49.71   7.526%   $53.4512   $53.45   $53.45   $53.50  
  Purchase #2 $242.36   13.472%   $275.0107   $275.01   $275.00   $275.00  
  Purchase #3 $124.91   8.640%   $135.7022   $135.70   $135.70   $135.70  
  Purchase #4 $45.53   4.591%   $47.6203   $47.62   $47.60   $47.60  
  Purchase #5 $211.60   10.658%   $234.1523   $234.15   $234.15   $234.20  
  Purchase #6 $194.70   11.517%   $217.1236   $217.12   $217.10   $217.10  
  Purchase #7 $111.41   7.459%   $119.7201   $119.72   $119.70   $119.70  
  7 purchase totals = $980.22       $1,082.7804   $1,082.77   $1,082.70   $1,082.80