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 $178.42   11.153%   $198.3192   $198.32   $198.30   $198.30  
  Purchase #2 $239.95   13.270%   $271.7914   $271.79   $271.80   $271.80  
  Purchase #3 $52.62   13.532%   $59.7405   $59.74   $59.75   $59.70  
  Purchase #4 $92.96   12.324%   $104.4164   $104.42   $104.40   $104.40  
  Purchase #5 $196.68   3.633%   $203.8254   $203.83   $203.85   $203.80  
  Purchase #6 $91.66   6.268%   $97.4052   $97.41   $97.40   $97.40  
  Purchase #7 $87.35   4.304%   $91.1095   $91.11   $91.10   $91.10  
  7 purchase totals = $939.64       $1,026.6076   $1,026.62   $1,026.60   $1,026.50