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 $191.68   6.769%   $204.6548   $204.65   $204.65   $204.70  
  Purchase #2 $133.61   3.678%   $138.5242   $138.52   $138.50   $138.50  
  Purchase #3 $158.90   6.381%   $169.0394   $169.04   $169.05   $169.00  
  Purchase #4 $196.51   4.560%   $205.4709   $205.47   $205.45   $205.50  
  Purchase #5 $60.96   11.355%   $67.882   $67.88   $67.90   $67.90  
  Purchase #6 $213.75   8.558%   $232.0427   $232.04   $232.05   $232.00  
  Purchase #7 $233.75   5.317%   $246.1785   $246.18   $246.20   $246.20  
  7 purchase totals = $1,189.16       $1,263.7925   $1,263.78   $1,263.80   $1,263.80