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 $118.87   10.446%   $131.2872   $131.29   $131.30   $131.30  
  Purchase #2 $60.38   13.143%   $68.3157   $68.32   $68.30   $68.30  
  Purchase #3 $59.37   5.846%   $62.8408   $62.84   $62.85   $62.80  
  Purchase #4 $152.44   9.748%   $167.2999   $167.30   $167.30   $167.30  
  Purchase #5 $122.88   5.873%   $130.0967   $130.10   $130.10   $130.10  
  Purchase #6 $189.68   4.792%   $198.7695   $198.77   $198.75   $198.80  
  Purchase #7 $73.60   5.840%   $77.8982   $77.90   $77.90   $77.90  
  7 purchase totals = $777.22       $836.5080   $836.52   $836.50   $836.50