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 $241.99   5.701%   $255.7858   $255.79   $255.80   $255.80  
  Purchase #2 $65.41   4.641%   $68.4457   $68.45   $68.45   $68.40  
  Purchase #3 $46.50   8.731%   $50.5599   $50.56   $50.55   $50.60  
  Purchase #4 $139.31   4.806%   $146.0052   $146.01   $146.00   $146.00  
  Purchase #5 $173.27   13.838%   $197.2471   $197.25   $197.25   $197.20  
  Purchase #6 $246.55   6.484%   $262.5363   $262.54   $262.55   $262.50  
  Purchase #7 $79.47   4.717%   $83.2186   $83.22   $83.20   $83.20  
  7 purchase totals = $992.50       $1,063.7986   $1,063.82   $1,063.80   $1,063.70