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 $73.84   12.232%   $82.8721   $82.87   $82.85   $82.90  
  Purchase #2 $209.31   8.666%   $227.4488   $227.45   $227.45   $227.40  
  Purchase #3 $108.58   10.219%   $119.6758   $119.68   $119.70   $119.70  
  Purchase #4 $216.30   12.868%   $244.1335   $244.13   $244.15   $244.10  
  Purchase #5 $174.47   5.567%   $184.1827   $184.18   $184.20   $184.20  
  Purchase #6 $123.26   3.635%   $127.7405   $127.74   $127.75   $127.70  
  Purchase #7 $66.36   11.383%   $73.9138   $73.91   $73.90   $73.90  
  7 purchase totals = $972.12       $1,059.9672   $1,059.96   $1,060.00   $1,059.90