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 $55.54   8.378%   $60.1931   $60.19   $60.20   $60.20  
  Purchase #2 $169.63   10.388%   $187.2512   $187.25   $187.25   $187.30  
  Purchase #3 $99.49   6.522%   $105.9787   $105.98   $106.00   $106.00  
  Purchase #4 $120.93   5.609%   $127.713   $127.71   $127.70   $127.70  
  Purchase #5 $29.72   6.679%   $31.705   $31.71   $31.70   $31.70  
  Purchase #6 $108.64   10.736%   $120.3036   $120.30   $120.30   $120.30  
  Purchase #7 $126.47   3.414%   $130.7877   $130.79   $130.80   $130.80  
  7 purchase totals = $710.42       $763.9323   $763.93   $763.95   $764.00