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 $88.47   8.410%   $95.9103   $95.91   $95.90   $95.90  
  Purchase #2 $39.85   13.631%   $45.282   $45.28   $45.30   $45.30  
  Purchase #3 $133.64   10.446%   $147.6   $147.60   $147.60   $147.60  
  Purchase #4 $178.98   5.687%   $189.1586   $189.16   $189.15   $189.20  
  Purchase #5 $204.62   13.522%   $232.2887   $232.29   $232.30   $232.30  
  Purchase #6 $120.28   5.269%   $126.6176   $126.62   $126.60   $126.60  
  Purchase #7 $62.62   4.563%   $65.4774   $65.48   $65.50   $65.50  
  7 purchase totals = $828.46       $902.3346   $902.34   $902.35   $902.40