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 $106.74   13.115%   $120.739   $120.74   $120.75   $120.70  
  Purchase #2 $216.32   3.479%   $223.8458   $223.85   $223.85   $223.80  
  Purchase #3 $156.72   13.661%   $178.1295   $178.13   $178.15   $178.10  
  Purchase #4 $82.34   12.358%   $92.5156   $92.52   $92.50   $92.50  
  Purchase #5 $189.36   10.865%   $209.934   $209.93   $209.95   $209.90  
  Purchase #6 $142.57   9.540%   $156.1712   $156.17   $156.15   $156.20  
  Purchase #7 $163.50   4.354%   $170.6188   $170.62   $170.60   $170.60  
  7 purchase totals = $1,057.55       $1,151.9539   $1,151.96   $1,151.95   $1,151.80