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 $98.68   10.633%   $109.1726   $109.17   $109.15   $109.20  
  Purchase #2 $172.51   3.645%   $178.798   $178.80   $178.80   $178.80  
  Purchase #3 $200.95   4.397%   $209.7858   $209.79   $209.80   $209.80  
  Purchase #4 $147.77   3.515%   $152.9641   $152.96   $152.95   $153.00  
  Purchase #5 $226.53   5.419%   $238.8057   $238.81   $238.80   $238.80  
  Purchase #6 $173.67   10.393%   $191.7195   $191.72   $191.70   $191.70  
  Purchase #7 $35.39   12.686%   $39.8796   $39.88   $39.90   $39.90  
  7 purchase totals = $1,055.50       $1,121.1253   $1,121.13   $1,121.10   $1,121.20