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 $57.65   8.621%   $62.62   $62.62   $62.60   $62.60  
  Purchase #2 $217.25   8.236%   $235.1427   $235.14   $235.15   $235.10  
  Purchase #3 $202.60   7.796%   $218.3947   $218.39   $218.40   $218.40  
  Purchase #4 $38.45   10.273%   $42.4   $42.40   $42.40   $42.40  
  Purchase #5 $228.84   9.872%   $251.4311   $251.43   $251.45   $251.40  
  Purchase #6 $204.36   7.484%   $219.6543   $219.65   $219.65   $219.70  
  Purchase #7 $33.36   9.665%   $36.5842   $36.58   $36.60   $36.60  
  7 purchase totals = $982.51       $1,066.2270   $1,066.21   $1,066.25   $1,066.20