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 $147.94   9.257%   $161.6348   $161.63   $161.65   $161.60  
  Purchase #2 $203.92   10.696%   $225.7313   $225.73   $225.75   $225.70  
  Purchase #3 $218.52   6.373%   $232.4463   $232.45   $232.45   $232.40  
  Purchase #4 $197.73   5.256%   $208.1227   $208.12   $208.10   $208.10  
  Purchase #5 $100.28   9.621%   $109.9279   $109.93   $109.95   $109.90  
  Purchase #6 $202.41   6.862%   $216.2994   $216.30   $216.30   $216.30  
  Purchase #7 $185.38   4.716%   $194.1225   $194.12   $194.10   $194.10  
  7 purchase totals = $1,256.18       $1,348.2849   $1,348.28   $1,348.30   $1,348.10