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 $223.54   7.479%   $240.2586   $240.26   $240.25   $240.30  
  Purchase #2 $201.98   13.526%   $229.2998   $229.30   $229.30   $229.30  
  Purchase #3 $143.85   5.210%   $151.3446   $151.34   $151.35   $151.30  
  Purchase #4 $89.88   4.459%   $93.8877   $93.89   $93.90   $93.90  
  Purchase #5 $179.96   6.502%   $191.661   $191.66   $191.65   $191.70  
  Purchase #6 $182.53   4.193%   $190.1835   $190.18   $190.20   $190.20  
  Purchase #7 $212.61   6.395%   $226.2064   $226.21   $226.20   $226.20  
  7 purchase totals = $1,234.35       $1,322.8416   $1,322.84   $1,322.85   $1,322.90