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 $130.54   13.723%   $148.454   $148.45   $148.45   $148.50  
  Purchase #2 $67.73   13.659%   $76.9812   $76.98   $77.00   $77.00  
  Purchase #3 $181.92   4.247%   $189.6461   $189.65   $189.65   $189.60  
  Purchase #4 $153.45   10.160%   $169.0405   $169.04   $169.05   $169.00  
  Purchase #5 $180.51   12.655%   $203.3535   $203.35   $203.35   $203.40  
  Purchase #6 $92.96   13.124%   $105.1601   $105.16   $105.15   $105.20  
  Purchase #7 $157.42   6.438%   $167.5547   $167.55   $167.55   $167.60  
  7 purchase totals = $964.53       $1,060.1901   $1,060.18   $1,060.20   $1,060.30