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 $232.88   13.459%   $264.2233   $264.22   $264.20   $264.20  
  Purchase #2 $234.95   9.675%   $257.6814   $257.68   $257.70   $257.70  
  Purchase #3 $244.29   12.442%   $274.6846   $274.68   $274.70   $274.70  
  Purchase #4 $6.40   11.468%   $7.134   $7.13   $7.15   $7.10  
  Purchase #5 $168.52   10.336%   $185.9382   $185.94   $185.95   $185.90  
  Purchase #6 $176.85   4.412%   $184.6526   $184.65   $184.65   $184.70  
  Purchase #7 $172.51   7.176%   $184.8893   $184.89   $184.90   $184.90  
  7 purchase totals = $1,236.40       $1,359.2034   $1,359.19   $1,359.25   $1,359.20