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 $237.32   12.779%   $267.6471   $267.65   $267.65   $267.60  
  Purchase #2 $53.78   12.380%   $60.438   $60.44   $60.45   $60.40  
  Purchase #3 $237.71   6.132%   $252.2864   $252.29   $252.30   $252.30  
  Purchase #4 $111.34   12.666%   $125.4423   $125.44   $125.45   $125.40  
  Purchase #5 $206.99   10.408%   $228.5335   $228.53   $228.55   $228.50  
  Purchase #6 $24.90   5.159%   $26.1846   $26.18   $26.20   $26.20  
  Purchase #7 $62.96   3.435%   $65.1227   $65.12   $65.10   $65.10  
  7 purchase totals = $935.00       $1,025.6546   $1,025.65   $1,025.70   $1,025.50