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 $178.47   13.864%   $203.2131   $203.21   $203.20   $203.20  
  Purchase #2 $129.43   11.278%   $144.0271   $144.03   $144.05   $144.00  
  Purchase #3 $11.71   7.616%   $12.6018   $12.60   $12.60   $12.60  
  Purchase #4 $96.53   5.548%   $101.8855   $101.89   $101.90   $101.90  
  Purchase #5 $186.79   11.136%   $207.5909   $207.59   $207.60   $207.60  
  Purchase #6 $233.73   12.823%   $263.7012   $263.70   $263.70   $263.70  
  Purchase #7 $117.55   4.719%   $123.0972   $123.10   $123.10   $123.10  
  7 purchase totals = $954.21       $1,056.1168   $1,056.12   $1,056.15   $1,056.10