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 $46.67   5.421%   $49.2   $49.20   $49.20   $49.20  
  Purchase #2 $23.55   11.791%   $26.3268   $26.33   $26.35   $26.30  
  Purchase #3 $141.88   6.153%   $150.6099   $150.61   $150.60   $150.60  
  Purchase #4 $200.74   6.676%   $214.1414   $214.14   $214.15   $214.10  
  Purchase #5 $198.74   8.178%   $214.993   $214.99   $215.00   $215.00  
  Purchase #6 $64.38   11.631%   $71.868   $71.87   $71.85   $71.90  
  Purchase #7 $210.85   7.221%   $226.0755   $226.08   $226.10   $226.10  
  7 purchase totals = $886.81       $953.2146   $953.22   $953.25   $953.20