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 $55.34   3.610%   $57.3378   $57.34   $57.35   $57.30  
  Purchase #2 $192.59   5.795%   $203.7506   $203.75   $203.75   $203.80  
  Purchase #3 $55.33   3.262%   $57.1349   $57.13   $57.15   $57.10  
  Purchase #4 $221.27   4.226%   $230.6209   $230.62   $230.60   $230.60  
  Purchase #5 $189.27   6.160%   $200.929   $200.93   $200.95   $200.90  
  Purchase #6 $158.66   6.389%   $168.7968   $168.80   $168.80   $168.80  
  Purchase #7 $80.89   8.816%   $88.0213   $88.02   $88.00   $88.00  
  7 purchase totals = $953.35       $1,006.5913   $1,006.59   $1,006.60   $1,006.50