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 $193.39   4.152%   $201.4196   $201.42   $201.40   $201.40  
  Purchase #2 $204.62   5.831%   $216.5514   $216.55   $216.55   $216.60  
  Purchase #3 $62.50   13.245%   $70.7781   $70.78   $70.80   $70.80  
  Purchase #4 $8.58   6.353%   $9.1251   $9.13   $9.15   $9.10  
  Purchase #5 $184.80   13.236%   $209.2601   $209.26   $209.25   $209.30  
  Purchase #6 $213.79   12.794%   $241.1423   $241.14   $241.15   $241.10  
  Purchase #7 $5.27   7.556%   $5.6682   $5.67   $5.65   $5.70  
  7 purchase totals = $872.95       $953.9448   $953.95   $953.95   $954.00