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 $120.77   10.731%   $133.7298   $133.73   $133.75   $133.70  
  Purchase #2 $211.44   7.108%   $226.4692   $226.47   $226.45   $226.50  
  Purchase #3 $66.39   12.170%   $74.4697   $74.47   $74.45   $74.50  
  Purchase #4 $211.69   11.410%   $235.8438   $235.84   $235.85   $235.80  
  Purchase #5 $189.59   7.867%   $204.505   $204.51   $204.50   $204.50  
  Purchase #6 $56.68   4.697%   $59.3423   $59.34   $59.35   $59.30  
  Purchase #7 $246.81   5.435%   $260.2241   $260.22   $260.20   $260.20  
  7 purchase totals = $1,103.37       $1,194.5839   $1,194.58   $1,194.55   $1,194.50