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 $106.84   11.511%   $119.1384   $119.14   $119.15   $119.10  
  Purchase #2 $220.44   13.718%   $250.68   $250.68   $250.70   $250.70  
  Purchase #3 $120.51   4.246%   $125.6269   $125.63   $125.65   $125.60  
  Purchase #4 $206.47   9.439%   $225.9587   $225.96   $225.95   $226.00  
  Purchase #5 $148.30   3.700%   $153.7871   $153.79   $153.80   $153.80  
  Purchase #6 $115.99   11.686%   $129.5446   $129.54   $129.55   $129.50  
  Purchase #7 $48.52   13.844%   $55.2371   $55.24   $55.25   $55.20  
  7 purchase totals = $967.07       $1,059.9728   $1,059.98   $1,060.05   $1,059.90