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 $233.48   3.473%   $241.5888   $241.59   $241.60   $241.60  
  Purchase #2 $138.64   3.807%   $143.918   $143.92   $143.90   $143.90  
  Purchase #3 $52.94   13.609%   $60.1446   $60.14   $60.15   $60.10  
  Purchase #4 $170.43   5.496%   $179.7968   $179.80   $179.80   $179.80  
  Purchase #5 $116.48   10.752%   $129.0039   $129.00   $129.00   $129.00  
  Purchase #6 $223.79   3.633%   $231.9203   $231.92   $231.90   $231.90  
  Purchase #7 $25.58   8.103%   $27.6527   $27.65   $27.65   $27.70  
  7 purchase totals = $961.34       $1,014.0251   $1,014.02   $1,014.00   $1,014.00