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 $52.37   12.173%   $58.745   $58.75   $58.75   $58.70  
  Purchase #2 $80.78   13.333%   $91.5504   $91.55   $91.55   $91.60  
  Purchase #3 $108.89   5.813%   $115.2198   $115.22   $115.20   $115.20  
  Purchase #4 $157.88   9.199%   $172.4034   $172.40   $172.40   $172.40  
  Purchase #5 $70.92   11.184%   $78.8517   $78.85   $78.85   $78.90  
  Purchase #6 $216.33   12.718%   $243.8428   $243.84   $243.85   $243.80  
  Purchase #7 $184.61   9.137%   $201.4778   $201.48   $201.50   $201.50  
  7 purchase totals = $871.78       $962.0909   $962.09   $962.10   $962.10