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 $246.91   8.566%   $268.0603   $268.06   $268.05   $268.10  
  Purchase #2 $137.63   12.472%   $154.7952   $154.80   $154.80   $154.80  
  Purchase #3 $243.43   9.122%   $265.6357   $265.64   $265.65   $265.60  
  Purchase #4 $7.78   6.225%   $8.2643   $8.26   $8.25   $8.30  
  Purchase #5 $60.58   12.471%   $68.1349   $68.13   $68.15   $68.10  
  Purchase #6 $108.99   3.525%   $112.8319   $112.83   $112.85   $112.80  
  Purchase #7 $150.93   9.753%   $165.6502   $165.65   $165.65   $165.70  
  7 purchase totals = $956.25       $1,043.3725   $1,043.37   $1,043.40   $1,043.40