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 $119.98   13.514%   $136.1941   $136.19   $136.20   $136.20  
  Purchase #2 $184.78   12.499%   $207.8757   $207.88   $207.90   $207.90  
  Purchase #3 $45.60   5.740%   $48.2174   $48.22   $48.20   $48.20  
  Purchase #4 $130.86   9.193%   $142.89   $142.89   $142.90   $142.90  
  Purchase #5 $110.96   9.397%   $121.3869   $121.39   $121.40   $121.40  
  Purchase #6 $155.64   3.645%   $161.3131   $161.31   $161.30   $161.30  
  Purchase #7 $24.76   10.307%   $27.312   $27.31   $27.30   $27.30  
  7 purchase totals = $772.58       $845.1892   $845.19   $845.20   $845.20