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 $204.53   12.768%   $230.6444   $230.64   $230.65   $230.60  
  Purchase #2 $195.60   5.439%   $206.2387   $206.24   $206.25   $206.20  
  Purchase #3 $171.94   12.374%   $193.2159   $193.22   $193.20   $193.20  
  Purchase #4 $17.85   3.268%   $18.4333   $18.43   $18.45   $18.40  
  Purchase #5 $128.52   6.449%   $136.8083   $136.81   $136.80   $136.80  
  Purchase #6 $45.99   10.830%   $50.9707   $50.97   $50.95   $51.00  
  Purchase #7 $162.65   9.502%   $178.105   $178.11   $178.10   $178.10  
  7 purchase totals = $927.08       $1,014.4163   $1,014.42   $1,014.40   $1,014.30