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 $88.67   6.641%   $94.5586   $94.56   $94.55   $94.60  
  Purchase #2 $31.92   13.390%   $36.1941   $36.19   $36.20   $36.20  
  Purchase #3 $227.65   3.570%   $235.7771   $235.78   $235.80   $235.80  
  Purchase #4 $94.57   6.499%   $100.7161   $100.72   $100.70   $100.70  
  Purchase #5 $234.32   13.778%   $266.6046   $266.60   $266.60   $266.60  
  Purchase #6 $101.60   5.132%   $106.8141   $106.81   $106.80   $106.80  
  Purchase #7 $173.63   5.745%   $183.605   $183.61   $183.60   $183.60  
  7 purchase totals = $952.36       $1,024.2696   $1,024.27   $1,024.25   $1,024.30