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 $105.71   11.792%   $118.1753   $118.18   $118.20   $118.20  
  Purchase #2 $232.68   9.480%   $254.7381   $254.74   $254.75   $254.70  
  Purchase #3 $22.39   11.213%   $24.9006   $24.90   $24.90   $24.90  
  Purchase #4 $158.66   9.710%   $174.0659   $174.07   $174.05   $174.10  
  Purchase #5 $104.86   10.649%   $116.0265   $116.03   $116.05   $116.00  
  Purchase #6 $149.29   4.649%   $156.2305   $156.23   $156.25   $156.20  
  Purchase #7 $172.78   3.278%   $178.4437   $178.44   $178.45   $178.40  
  7 purchase totals = $946.37       $1,022.5806   $1,022.59   $1,022.65   $1,022.50