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 $59.60   11.624%   $66.5279   $66.53   $66.55   $66.50  
  Purchase #2 $193.59   9.114%   $211.2338   $211.23   $211.25   $211.20  
  Purchase #3 $18.80   8.339%   $20.3677   $20.37   $20.35   $20.40  
  Purchase #4 $206.55   6.167%   $219.2879   $219.29   $219.30   $219.30  
  Purchase #5 $162.71   7.769%   $175.3509   $175.35   $175.35   $175.40  
  Purchase #6 $101.56   7.320%   $108.9942   $108.99   $109.00   $109.00  
  Purchase #7 $87.98   8.205%   $95.1988   $95.20   $95.20   $95.20  
  7 purchase totals = $830.79       $896.9612   $896.96   $897.00   $897.00