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 $136.55   9.603%   $149.6629   $149.66   $149.65   $149.70  
  Purchase #2 $174.29   6.366%   $185.3853   $185.39   $185.40   $185.40  
  Purchase #3 $135.84   8.203%   $146.983   $146.98   $147.00   $147.00  
  Purchase #4 $98.86   9.661%   $108.4109   $108.41   $108.40   $108.40  
  Purchase #5 $24.34   6.711%   $25.9735   $25.97   $25.95   $26.00  
  Purchase #6 $13.35   11.598%   $14.8983   $14.90   $14.90   $14.90  
  Purchase #7 $108.86   11.430%   $121.3027   $121.30   $121.30   $121.30  
  7 purchase totals = $692.09       $752.6166   $752.61   $752.60   $752.70