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 $174.75   11.412%   $194.6925   $194.69   $194.70   $194.70  
  Purchase #2 $219.41   12.707%   $247.2904   $247.29   $247.30   $247.30  
  Purchase #3 $97.29   9.687%   $106.7145   $106.71   $106.70   $106.70  
  Purchase #4 $43.60   7.828%   $47.013   $47.01   $47.00   $47.00  
  Purchase #5 $247.63   3.727%   $256.8592   $256.86   $256.85   $256.90  
  Purchase #6 $216.82   13.775%   $246.687   $246.69   $246.70   $246.70  
  Purchase #7 $212.83   3.608%   $220.5089   $220.51   $220.50   $220.50  
  7 purchase totals = $1,212.33       $1,319.7655   $1,319.76   $1,319.75   $1,319.80