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 $177.53   11.672%   $198.2513   $198.25   $198.25   $198.30  
  Purchase #2 $215.80   5.761%   $228.2322   $228.23   $228.25   $228.20  
  Purchase #3 $153.33   5.689%   $162.0529   $162.05   $162.05   $162.10  
  Purchase #4 $124.71   9.315%   $136.3267   $136.33   $136.35   $136.30  
  Purchase #5 $17.95   9.544%   $19.6631   $19.66   $19.65   $19.70  
  Purchase #6 $34.34   5.842%   $36.3461   $36.35   $36.35   $36.30  
  Purchase #7 $242.72   11.545%   $270.742   $270.74   $270.75   $270.70  
  7 purchase totals = $966.38       $1,051.6143   $1,051.61   $1,051.65   $1,051.60