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 $115.59   8.443%   $125.3493   $125.35   $125.35   $125.30  
  Purchase #2 $149.44   10.529%   $165.1745   $165.17   $165.15   $165.20  
  Purchase #3 $114.26   10.455%   $126.2059   $126.21   $126.20   $126.20  
  Purchase #4 $42.61   5.626%   $45.0072   $45.01   $45.00   $45.00  
  Purchase #5 $121.69   3.222%   $125.6109   $125.61   $125.60   $125.60  
  Purchase #6 $214.33   8.858%   $233.3154   $233.32   $233.30   $233.30  
  Purchase #7 $203.54   5.180%   $214.0834   $214.08   $214.10   $214.10  
  7 purchase totals = $961.46       $1,034.7466   $1,034.75   $1,034.70   $1,034.70