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 $53.57   5.736%   $56.6428   $56.64   $56.65   $56.60  
  Purchase #2 $61.34   3.187%   $63.2949   $63.29   $63.30   $63.30  
  Purchase #3 $210.72   8.229%   $228.0601   $228.06   $228.05   $228.10  
  Purchase #4 $182.53   12.425%   $205.2094   $205.21   $205.20   $205.20  
  Purchase #5 $26.52   4.588%   $27.7367   $27.74   $27.75   $27.70  
  Purchase #6 $248.82   5.217%   $261.8009   $261.80   $261.80   $261.80  
  Purchase #7 $65.34   7.225%   $70.0608   $70.06   $70.05   $70.10  
  7 purchase totals = $848.84       $912.8056   $912.80   $912.80   $912.80