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 $92.66   13.561%   $105.2256   $105.23   $105.25   $105.20  
  Purchase #2 $191.52   7.133%   $205.1811   $205.18   $205.20   $205.20  
  Purchase #3 $247.77   3.177%   $255.6417   $255.64   $255.65   $255.60  
  Purchase #4 $23.65   12.121%   $26.5166   $26.52   $26.50   $26.50  
  Purchase #5 $204.32   13.186%   $231.2616   $231.26   $231.25   $231.30  
  Purchase #6 $236.55   13.242%   $267.874   $267.87   $267.85   $267.90  
  Purchase #7 $26.84   6.716%   $28.6426   $28.64   $28.65   $28.60  
  7 purchase totals = $1,023.31       $1,120.3432   $1,120.34   $1,120.35   $1,120.30