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 $61.84   11.156%   $68.7389   $68.74   $68.75   $68.70  
  Purchase #2 $185.97   6.563%   $198.1752   $198.18   $198.20   $198.20  
  Purchase #3 $120.76   7.213%   $129.4704   $129.47   $129.45   $129.50  
  Purchase #4 $19.28   6.414%   $20.5166   $20.52   $20.50   $20.50  
  Purchase #5 $191.32   6.537%   $203.8266   $203.83   $203.85   $203.80  
  Purchase #6 $172.89   11.709%   $193.1337   $193.13   $193.15   $193.10  
  Purchase #7 $238.83   8.566%   $259.2882   $259.29   $259.30   $259.30  
  7 purchase totals = $990.89       $1,073.1496   $1,073.16   $1,073.20   $1,073.10