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 $49.97   7.586%   $53.7607   $53.76   $53.75   $53.80  
  Purchase #2 $170.59   12.173%   $191.3559   $191.36   $191.35   $191.40  
  Purchase #3 $120.73   7.598%   $129.9031   $129.90   $129.90   $129.90  
  Purchase #4 $195.94   7.661%   $210.951   $210.95   $210.95   $211.00  
  Purchase #5 $161.92   9.761%   $177.725   $177.73   $177.75   $177.70  
  Purchase #6 $203.63   13.433%   $230.9836   $230.98   $231.00   $231.00  
  Purchase #7 $79.29   11.682%   $88.5527   $88.55   $88.55   $88.60  
  7 purchase totals = $982.07       $1,083.2320   $1,083.23   $1,083.25   $1,083.40