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 $88.81   6.864%   $94.9059   $94.91   $94.90   $94.90  
  Purchase #2 $14.34   4.203%   $14.9427   $14.94   $14.95   $14.90  
  Purchase #3 $171.78   10.513%   $189.8392   $189.84   $189.85   $189.80  
  Purchase #4 $34.36   12.347%   $38.6024   $38.60   $38.60   $38.60  
  Purchase #5 $189.73   9.244%   $207.2686   $207.27   $207.25   $207.30  
  Purchase #6 $180.52   5.830%   $191.0443   $191.04   $191.05   $191.00  
  Purchase #7 $106.69   10.191%   $117.5628   $117.56   $117.55   $117.60  
  7 purchase totals = $786.23       $854.1659   $854.16   $854.15   $854.10