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 $48.74   10.328%   $53.7739   $53.77   $53.75   $53.80  
  Purchase #2 $200.84   5.535%   $211.9565   $211.96   $211.95   $212.00  
  Purchase #3 $230.78   13.494%   $261.9215   $261.92   $261.90   $261.90  
  Purchase #4 $157.72   9.596%   $172.8548   $172.85   $172.85   $172.90  
  Purchase #5 $18.49   9.142%   $20.1804   $20.18   $20.20   $20.20  
  Purchase #6 $187.69   9.169%   $204.8993   $204.90   $204.90   $204.90  
  Purchase #7 $170.98   7.635%   $184.0343   $184.03   $184.05   $184.00  
  7 purchase totals = $1,015.24       $1,109.6207   $1,109.61   $1,109.60   $1,109.70