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 $75.25   11.776%   $84.1114   $84.11   $84.10   $84.10  
  Purchase #2 $163.33   5.826%   $172.8456   $172.85   $172.85   $172.80  
  Purchase #3 $183.98   10.870%   $203.9786   $203.98   $204.00   $204.00  
  Purchase #4 $208.83   10.576%   $230.9159   $230.92   $230.90   $230.90  
  Purchase #5 $50.41   10.236%   $55.57   $55.57   $55.55   $55.60  
  Purchase #6 $148.51   12.741%   $167.4317   $167.43   $167.45   $167.40  
  Purchase #7 $95.35   9.729%   $104.6266   $104.63   $104.65   $104.60  
  7 purchase totals = $925.66       $1,019.4798   $1,019.49   $1,019.50   $1,019.40