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 $96.29   9.864%   $105.788   $105.79   $105.80   $105.80  
  Purchase #2 $102.31   8.154%   $110.6524   $110.65   $110.65   $110.70  
  Purchase #3 $117.93   11.533%   $131.5309   $131.53   $131.55   $131.50  
  Purchase #4 $41.74   7.150%   $44.7244   $44.72   $44.70   $44.70  
  Purchase #5 $98.51   7.250%   $105.652   $105.65   $105.65   $105.70  
  Purchase #6 $136.76   6.245%   $145.3007   $145.30   $145.30   $145.30  
  Purchase #7 $72.92   9.665%   $79.9677   $79.97   $79.95   $80.00  
  7 purchase totals = $666.46       $723.6161   $723.61   $723.60   $723.70