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 $59.69   5.721%   $63.1049   $63.10   $63.10   $63.10  
  Purchase #2 $225.31   9.512%   $246.7415   $246.74   $246.75   $246.70  
  Purchase #3 $242.58   7.482%   $260.7298   $260.73   $260.75   $260.70  
  Purchase #4 $45.45   11.705%   $50.7699   $50.77   $50.75   $50.80  
  Purchase #5 $78.43   13.227%   $88.8039   $88.80   $88.80   $88.80  
  Purchase #6 $6.29   5.458%   $6.6333   $6.63   $6.65   $6.60  
  Purchase #7 $226.54   11.118%   $251.7267   $251.73   $251.75   $251.70  
  7 purchase totals = $884.29       $968.5100   $968.50   $968.55   $968.40