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 $225.53   12.541%   $253.8137   $253.81   $253.80   $253.80  
  Purchase #2 $210.29   6.459%   $223.8726   $223.87   $223.85   $223.90  
  Purchase #3 $174.83   13.290%   $198.0649   $198.06   $198.05   $198.10  
  Purchase #4 $245.47   5.830%   $259.7809   $259.78   $259.80   $259.80  
  Purchase #5 $43.44   3.624%   $45.0143   $45.01   $45.00   $45.00  
  Purchase #6 $136.43   9.625%   $149.5614   $149.56   $149.55   $149.60  
  Purchase #7 $64.72   10.720%   $71.658   $71.66   $71.65   $71.70  
  7 purchase totals = $1,100.71       $1,201.7658   $1,201.75   $1,201.70   $1,201.90