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 $65.82   12.854%   $74.2805   $74.28   $74.30   $74.30  
  Purchase #2 $108.66   7.530%   $116.8421   $116.84   $116.85   $116.80  
  Purchase #3 $196.54   4.365%   $205.119   $205.12   $205.10   $205.10  
  Purchase #4 $190.84   11.851%   $213.4564   $213.46   $213.45   $213.50  
  Purchase #5 $94.53   12.170%   $106.0343   $106.03   $106.05   $106.00  
  Purchase #6 $232.54   11.179%   $258.5356   $258.54   $258.55   $258.50  
  Purchase #7 $219.76   4.235%   $229.0668   $229.07   $229.05   $229.10  
  7 purchase totals = $1,108.69       $1,203.3347   $1,203.34   $1,203.35   $1,203.30