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 $211.51   12.477%   $237.9001   $237.90   $237.90   $237.90  
  Purchase #2 $114.71   10.262%   $126.4815   $126.48   $126.50   $126.50  
  Purchase #3 $53.37   6.798%   $56.9981   $57.00   $57.00   $57.00  
  Purchase #4 $138.66   10.581%   $153.3316   $153.33   $153.35   $153.30  
  Purchase #5 $149.79   10.473%   $165.4775   $165.48   $165.50   $165.50  
  Purchase #6 $223.77   13.313%   $253.5605   $253.56   $253.55   $253.60  
  Purchase #7 $86.86   13.791%   $98.8389   $98.84   $98.85   $98.80  
  7 purchase totals = $978.67       $1,092.5882   $1,092.59   $1,092.65   $1,092.60