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 $69.74   7.868%   $75.2271   $75.23   $75.25   $75.20  
  Purchase #2 $248.31   8.107%   $268.4405   $268.44   $268.45   $268.40  
  Purchase #3 $138.29   10.222%   $152.426   $152.43   $152.45   $152.40  
  Purchase #4 $27.75   3.130%   $28.6186   $28.62   $28.60   $28.60  
  Purchase #5 $185.25   8.117%   $200.2867   $200.29   $200.30   $200.30  
  Purchase #6 $60.96   6.175%   $64.7243   $64.72   $64.70   $64.70  
  Purchase #7 $244.73   10.241%   $269.7928   $269.79   $269.80   $269.80  
  7 purchase totals = $975.03       $1,059.5160   $1,059.52   $1,059.55   $1,059.40