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 $91.92   13.520%   $104.3476   $104.35   $104.35   $104.30  
  Purchase #2 $211.76   11.759%   $236.6609   $236.66   $236.65   $236.70  
  Purchase #3 $150.95   11.183%   $167.8307   $167.83   $167.85   $167.80  
  Purchase #4 $246.94   7.805%   $266.2137   $266.21   $266.20   $266.20  
  Purchase #5 $147.28   10.593%   $162.8814   $162.88   $162.90   $162.90  
  Purchase #6 $80.29   13.212%   $90.8979   $90.90   $90.90   $90.90  
  Purchase #7 $129.78   5.490%   $136.9049   $136.90   $136.90   $136.90  
  7 purchase totals = $1,058.92       $1,165.7371   $1,165.73   $1,165.75   $1,165.70