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 $175.59   9.302%   $191.9234   $191.92   $191.90   $191.90  
  Purchase #2 $23.97   3.362%   $24.7759   $24.78   $24.80   $24.80  
  Purchase #3 $93.98   9.161%   $102.5895   $102.59   $102.60   $102.60  
  Purchase #4 $233.25   6.171%   $247.6439   $247.64   $247.65   $247.60  
  Purchase #5 $210.36   5.256%   $221.4165   $221.42   $221.40   $221.40  
  Purchase #6 $165.80   9.839%   $182.1131   $182.11   $182.10   $182.10  
  Purchase #7 $224.92   3.471%   $232.727   $232.73   $232.75   $232.70  
  7 purchase totals = $1,127.87       $1,203.1893   $1,203.19   $1,203.20   $1,203.10