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 $160.84   11.531%   $179.3865   $179.39   $179.40   $179.40  
  Purchase #2 $106.39   12.380%   $119.5611   $119.56   $119.55   $119.60  
  Purchase #3 $34.35   9.620%   $37.6545   $37.65   $37.65   $37.70  
  Purchase #4 $213.32   10.808%   $236.3756   $236.38   $236.40   $236.40  
  Purchase #5 $221.95   10.829%   $245.985   $245.99   $246.00   $246.00  
  Purchase #6 $204.91   13.210%   $231.9786   $231.98   $232.00   $232.00  
  Purchase #7 $186.39   13.400%   $211.3663   $211.37   $211.35   $211.40  
  7 purchase totals = $1,128.15       $1,262.3076   $1,262.32   $1,262.35   $1,262.50