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 $101.96   6.606%   $108.6955   $108.70   $108.70   $108.70  
  Purchase #2 $196.82   3.354%   $203.4213   $203.42   $203.40   $203.40  
  Purchase #3 $227.80   7.325%   $244.4864   $244.49   $244.50   $244.50  
  Purchase #4 $125.37   8.244%   $135.7055   $135.71   $135.70   $135.70  
  Purchase #5 $122.52   13.284%   $138.7956   $138.80   $138.80   $138.80  
  Purchase #6 $34.32   6.502%   $36.5515   $36.55   $36.55   $36.60  
  Purchase #7 $161.95   12.543%   $182.2634   $182.26   $182.25   $182.30  
  7 purchase totals = $970.74       $1,049.9192   $1,049.93   $1,049.90   $1,050.00