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 $58.58   3.657%   $60.7223   $60.72   $60.70   $60.70  
  Purchase #2 $35.41   11.137%   $39.3536   $39.35   $39.35   $39.40  
  Purchase #3 $211.86   3.780%   $219.8683   $219.87   $219.85   $219.90  
  Purchase #4 $152.79   9.658%   $167.5465   $167.55   $167.55   $167.50  
  Purchase #5 $73.99   4.256%   $77.139   $77.14   $77.15   $77.10  
  Purchase #6 $242.71   5.441%   $255.9159   $255.92   $255.90   $255.90  
  Purchase #7 $179.78   12.144%   $201.6125   $201.61   $201.60   $201.60  
  7 purchase totals = $955.12       $1,022.1581   $1,022.16   $1,022.10   $1,022.10