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 $185.31   13.679%   $210.6586   $210.66   $210.65   $210.70  
  Purchase #2 $65.87   4.371%   $68.7492   $68.75   $68.75   $68.70  
  Purchase #3 $204.76   9.160%   $223.516   $223.52   $223.50   $223.50  
  Purchase #4 $168.40   10.757%   $186.5148   $186.51   $186.50   $186.50  
  Purchase #5 $107.60   13.666%   $122.3046   $122.30   $122.30   $122.30  
  Purchase #6 $191.56   13.823%   $218.0393   $218.04   $218.05   $218.00  
  Purchase #7 $29.75   13.259%   $33.6946   $33.69   $33.70   $33.70  
  7 purchase totals = $953.25       $1,063.4771   $1,063.47   $1,063.45   $1,063.40