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 $229.97   10.740%   $254.6688   $254.67   $254.65   $254.70  
  Purchase #2 $169.89   3.699%   $176.1742   $176.17   $176.15   $176.20  
  Purchase #3 $220.59   5.700%   $233.1636   $233.16   $233.15   $233.20  
  Purchase #4 $204.96   9.843%   $225.1342   $225.13   $225.15   $225.10  
  Purchase #5 $142.98   5.732%   $151.1756   $151.18   $151.20   $151.20  
  Purchase #6 $146.32   7.209%   $156.8682   $156.87   $156.85   $156.90  
  Purchase #7 $50.31   11.400%   $56.0453   $56.05   $56.05   $56.00  
  7 purchase totals = $1,165.02       $1,253.2299   $1,253.23   $1,253.20   $1,253.30