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 $102.93   10.245%   $113.4752   $113.48   $113.50   $113.50  
  Purchase #2 $209.54   9.131%   $228.6731   $228.67   $228.65   $228.70  
  Purchase #3 $246.38   4.145%   $256.5925   $256.59   $256.60   $256.60  
  Purchase #4 $212.45   6.377%   $225.9979   $226.00   $226.00   $226.00  
  Purchase #5 $51.76   3.709%   $53.6798   $53.68   $53.70   $53.70  
  Purchase #6 $237.51   3.482%   $245.7801   $245.78   $245.80   $245.80  
  Purchase #7 $60.60   6.223%   $64.3711   $64.37   $64.35   $64.40  
  7 purchase totals = $1,121.17       $1,188.5697   $1,188.57   $1,188.60   $1,188.70