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 $47.48   6.837%   $50.7262   $50.73   $50.75   $50.70  
  Purchase #2 $211.78   10.639%   $234.3113   $234.31   $234.30   $234.30  
  Purchase #3 $205.75   6.695%   $219.525   $219.53   $219.55   $219.50  
  Purchase #4 $238.85   3.323%   $246.787   $246.79   $246.80   $246.80  
  Purchase #5 $93.55   12.773%   $105.4991   $105.50   $105.50   $105.50  
  Purchase #6 $157.93   11.359%   $175.8693   $175.87   $175.85   $175.90  
  Purchase #7 $12.47   5.201%   $13.1186   $13.12   $13.10   $13.10  
  7 purchase totals = $967.81       $1,045.8365   $1,045.85   $1,045.85   $1,045.80