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 $60.42   12.506%   $67.9761   $67.98   $68.00   $68.00  
  Purchase #2 $41.41   11.704%   $46.2566   $46.26   $46.25   $46.30  
  Purchase #3 $31.46   4.644%   $32.921   $32.92   $32.90   $32.90  
  Purchase #4 $223.82   6.629%   $238.657   $238.66   $238.65   $238.70  
  Purchase #5 $77.35   10.387%   $85.3843   $85.38   $85.40   $85.40  
  Purchase #6 $150.90   6.759%   $161.0993   $161.10   $161.10   $161.10  
  Purchase #7 $216.90   11.355%   $241.529   $241.53   $241.55   $241.50  
  7 purchase totals = $802.26       $873.8233   $873.83   $873.85   $873.90