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 $64.79   10.803%   $71.7893   $71.79   $71.80   $71.80  
  Purchase #2 $166.92   7.714%   $179.7962   $179.80   $179.80   $179.80  
  Purchase #3 $151.85   12.370%   $170.6338   $170.63   $170.65   $170.60  
  Purchase #4 $170.74   13.529%   $193.8394   $193.84   $193.85   $193.80  
  Purchase #5 $186.48   13.539%   $211.7275   $211.73   $211.75   $211.70  
  Purchase #6 $139.71   8.776%   $151.9709   $151.97   $151.95   $152.00  
  Purchase #7 $63.68   8.561%   $69.1316   $69.13   $69.15   $69.10  
  7 purchase totals = $944.17       $1,048.8887   $1,048.89   $1,048.95   $1,048.80