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 $63.46   6.587%   $67.6401   $67.64   $67.65   $67.60  
  Purchase #2 $232.99   11.123%   $258.9055   $258.91   $258.90   $258.90  
  Purchase #3 $245.51   8.121%   $265.4479   $265.45   $265.45   $265.40  
  Purchase #4 $133.99   12.498%   $150.7361   $150.74   $150.75   $150.70  
  Purchase #5 $50.50   8.544%   $54.8147   $54.81   $54.80   $54.80  
  Purchase #6 $219.67   4.746%   $230.0955   $230.10   $230.10   $230.10  
  Purchase #7 $145.97   10.226%   $160.8969   $160.90   $160.90   $160.90  
  7 purchase totals = $1,092.09       $1,188.5367   $1,188.55   $1,188.55   $1,188.40