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 $106.72   11.364%   $118.8477   $118.85   $118.85   $118.80  
  Purchase #2 $106.97   8.139%   $115.6763   $115.68   $115.70   $115.70  
  Purchase #3 $207.74   12.833%   $234.3993   $234.40   $234.40   $234.40  
  Purchase #4 $248.46   7.753%   $267.7231   $267.72   $267.70   $267.70  
  Purchase #5 $31.61   10.760%   $35.0112   $35.01   $35.00   $35.00  
  Purchase #6 $203.98   6.133%   $216.4901   $216.49   $216.50   $216.50  
  Purchase #7 $165.87   12.285%   $186.2471   $186.25   $186.25   $186.20  
  7 purchase totals = $1,071.35       $1,174.3948   $1,174.40   $1,174.40   $1,174.30