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 $116.81   13.164%   $132.1869   $132.19   $132.20   $132.20  
  Purchase #2 $159.95   13.579%   $181.6696   $181.67   $181.65   $181.70  
  Purchase #3 $240.25   4.447%   $250.9339   $250.93   $250.95   $250.90  
  Purchase #4 $224.73   8.585%   $244.0231   $244.02   $244.00   $244.00  
  Purchase #5 $91.74   3.363%   $94.8252   $94.83   $94.85   $94.80  
  Purchase #6 $201.96   11.583%   $225.353   $225.35   $225.35   $225.40  
  Purchase #7 $6.93   9.686%   $7.6012   $7.60   $7.60   $7.60  
  7 purchase totals = $1,042.37       $1,136.5929   $1,136.59   $1,136.60   $1,136.60