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 $211.60   9.654%   $232.0279   $232.03   $232.05   $232.00  
  Purchase #2 $184.91   4.148%   $192.5801   $192.58   $192.60   $192.60  
  Purchase #3 $44.64   5.386%   $47.0443   $47.04   $47.05   $47.00  
  Purchase #4 $25.89   12.385%   $29.0965   $29.10   $29.10   $29.10  
  Purchase #5 $95.85   5.486%   $101.1083   $101.11   $101.10   $101.10  
  Purchase #6 $37.33   4.370%   $38.9613   $38.96   $38.95   $39.00  
  Purchase #7 $63.73   3.395%   $65.8936   $65.89   $65.90   $65.90  
  7 purchase totals = $663.95       $706.7120   $706.71   $706.75   $706.70