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 $155.83   8.283%   $168.7374   $168.74   $168.75   $168.70  
  Purchase #2 $83.60   13.110%   $94.56   $94.56   $94.55   $94.60  
  Purchase #3 $54.95   13.365%   $62.2941   $62.29   $62.30   $62.30  
  Purchase #4 $224.89   11.133%   $249.927   $249.93   $249.95   $249.90  
  Purchase #5 $135.53   5.657%   $143.1969   $143.20   $143.20   $143.20  
  Purchase #6 $111.92   8.338%   $121.2519   $121.25   $121.25   $121.30  
  Purchase #7 $228.59   5.129%   $240.3144   $240.31   $240.30   $240.30  
  7 purchase totals = $995.31       $1,080.2817   $1,080.28   $1,080.30   $1,080.30