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 $49.25   6.137%   $52.2725   $52.27   $52.25   $52.30  
  Purchase #2 $194.35   4.737%   $203.5564   $203.56   $203.55   $203.60  
  Purchase #3 $105.61   7.365%   $113.3882   $113.39   $113.40   $113.40  
  Purchase #4 $212.98   9.262%   $232.7062   $232.71   $232.70   $232.70  
  Purchase #5 $166.36   10.725%   $184.2021   $184.20   $184.20   $184.20  
  Purchase #6 $249.58   7.562%   $268.4532   $268.45   $268.45   $268.50  
  Purchase #7 $208.67   10.516%   $230.6137   $230.61   $230.60   $230.60  
  7 purchase totals = $1,186.80       $1,285.1923   $1,285.19   $1,285.15   $1,285.30