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 $61.60   10.461%   $68.044   $68.04   $68.05   $68.00  
  Purchase #2 $64.53   13.255%   $73.0835   $73.08   $73.10   $73.10  
  Purchase #3 $69.81   10.833%   $77.3725   $77.37   $77.35   $77.40  
  Purchase #4 $55.34   12.274%   $62.1324   $62.13   $62.15   $62.10  
  Purchase #5 $37.44   4.343%   $39.066   $39.07   $39.05   $39.10  
  Purchase #6 $114.56   7.381%   $123.0157   $123.02   $123.00   $123.00  
  Purchase #7 $53.98   11.333%   $60.0976   $60.10   $60.10   $60.10  
  7 purchase totals = $457.26       $502.8117   $502.81   $502.80   $502.80