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 $92.63   5.732%   $97.9396   $97.94   $97.95   $97.90  
  Purchase #2 $39.36   6.204%   $41.8019   $41.80   $41.80   $41.80  
  Purchase #3 $190.27   7.814%   $205.1377   $205.14   $205.15   $205.10  
  Purchase #4 $64.70   13.807%   $73.6331   $73.63   $73.65   $73.60  
  Purchase #5 $46.66   12.853%   $52.6572   $52.66   $52.65   $52.70  
  Purchase #6 $203.72   7.700%   $219.4064   $219.41   $219.40   $219.40  
  Purchase #7 $40.79   8.347%   $44.1947   $44.19   $44.20   $44.20  
  7 purchase totals = $678.13       $734.7706   $734.77   $734.80   $734.70