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 $203.27   11.172%   $225.9793   $225.98   $226.00   $226.00  
  Purchase #2 $160.72   3.384%   $166.1588   $166.16   $166.15   $166.20  
  Purchase #3 $194.25   5.416%   $204.7706   $204.77   $204.75   $204.80  
  Purchase #4 $148.88   9.137%   $162.4832   $162.48   $162.50   $162.50  
  Purchase #5 $88.52   7.462%   $95.1254   $95.13   $95.15   $95.10  
  Purchase #6 $232.67   4.855%   $243.9661   $243.97   $243.95   $244.00  
  Purchase #7 $230.88   8.556%   $250.6341   $250.63   $250.65   $250.60  
  7 purchase totals = $1,259.19       $1,349.1175   $1,349.12   $1,349.15   $1,349.20