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 $67.56   4.329%   $70.4847   $70.48   $70.50   $70.50  
  Purchase #2 $197.27   3.501%   $204.1764   $204.18   $204.20   $204.20  
  Purchase #3 $227.52   11.589%   $253.8873   $253.89   $253.90   $253.90  
  Purchase #4 $34.75   5.629%   $36.7061   $36.71   $36.70   $36.70  
  Purchase #5 $238.29   3.282%   $246.1107   $246.11   $246.10   $246.10  
  Purchase #6 $115.92   9.455%   $126.8802   $126.88   $126.90   $126.90  
  Purchase #7 $162.66   12.693%   $183.3064   $183.31   $183.30   $183.30  
  7 purchase totals = $1,043.97       $1,121.5518   $1,121.56   $1,121.60   $1,121.60