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 $219.54   10.657%   $242.9364   $242.94   $242.95   $242.90  
  Purchase #2 $111.69   9.257%   $122.0291   $122.03   $122.05   $122.00  
  Purchase #3 $112.63   12.185%   $126.354   $126.35   $126.35   $126.40  
  Purchase #4 $33.64   7.163%   $36.0496   $36.05   $36.05   $36.00  
  Purchase #5 $151.96   7.139%   $162.8084   $162.81   $162.80   $162.80  
  Purchase #6 $181.37   6.701%   $193.5236   $193.52   $193.50   $193.50  
  Purchase #7 $241.90   12.471%   $272.0673   $272.07   $272.05   $272.10  
  7 purchase totals = $1,052.73       $1,155.7684   $1,155.77   $1,155.75   $1,155.70