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 $246.59   10.347%   $272.1047   $272.10   $272.10   $272.10  
  Purchase #2 $95.71   6.870%   $102.2853   $102.29   $102.30   $102.30  
  Purchase #3 $215.61   7.237%   $231.2137   $231.21   $231.20   $231.20  
  Purchase #4 $149.62   3.788%   $155.2876   $155.29   $155.30   $155.30  
  Purchase #5 $118.88   12.567%   $133.8196   $133.82   $133.80   $133.80  
  Purchase #6 $24.32   4.848%   $25.499   $25.50   $25.50   $25.50  
  Purchase #7 $228.44   11.365%   $254.4022   $254.40   $254.40   $254.40  
  7 purchase totals = $1,079.17       $1,174.6121   $1,174.61   $1,174.60   $1,174.60