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 $43.42   3.499%   $44.9393   $44.94   $44.95   $44.90  
  Purchase #2 $29.72   9.349%   $32.4985   $32.50   $32.50   $32.50  
  Purchase #3 $249.96   10.275%   $275.6434   $275.64   $275.65   $275.60  
  Purchase #4 $170.60   8.137%   $184.4817   $184.48   $184.50   $184.50  
  Purchase #5 $147.29   10.586%   $162.8821   $162.88   $162.90   $162.90  
  Purchase #6 $50.28   11.767%   $56.1964   $56.20   $56.20   $56.20  
  Purchase #7 $147.58   12.235%   $165.6364   $165.64   $165.65   $165.60  
  7 purchase totals = $838.85       $922.2778   $922.28   $922.35   $922.20