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 $94.34   12.562%   $106.191   $106.19   $106.20   $106.20  
  Purchase #2 $24.43   4.781%   $25.598   $25.60   $25.60   $25.60  
  Purchase #3 $145.94   12.213%   $163.7637   $163.76   $163.75   $163.80  
  Purchase #4 $63.65   13.120%   $72.0009   $72.00   $72.00   $72.00  
  Purchase #5 $39.48   4.386%   $41.2116   $41.21   $41.20   $41.20  
  Purchase #6 $86.65   9.395%   $94.7908   $94.79   $94.80   $94.80  
  Purchase #7 $53.64   12.146%   $60.1551   $60.16   $60.15   $60.20  
  7 purchase totals = $508.13       $563.7111   $563.71   $563.70   $563.80