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 $201.76   11.769%   $225.5051   $225.51   $225.50   $225.50  
  Purchase #2 $29.28   6.263%   $31.1138   $31.11   $31.10   $31.10  
  Purchase #3 $80.82   13.504%   $91.7339   $91.73   $91.75   $91.70  
  Purchase #4 $246.26   12.716%   $277.5744   $277.57   $277.55   $277.60  
  Purchase #5 $181.94   10.727%   $201.4567   $201.46   $201.45   $201.50  
  Purchase #6 $44.99   11.196%   $50.0271   $50.03   $50.05   $50.00  
  Purchase #7 $59.84   7.186%   $64.1401   $64.14   $64.15   $64.10  
  7 purchase totals = $844.89       $941.5511   $941.55   $941.55   $941.50