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 $244.68   6.374%   $260.2759   $260.28   $260.30   $260.30  
  Purchase #2 $123.76   6.409%   $131.6918   $131.69   $131.70   $131.70  
  Purchase #3 $90.96   13.588%   $103.3196   $103.32   $103.30   $103.30  
  Purchase #4 $122.64   5.704%   $129.6354   $129.64   $129.65   $129.60  
  Purchase #5 $119.38   13.580%   $135.5918   $135.59   $135.60   $135.60  
  Purchase #6 $181.77   3.221%   $187.6248   $187.62   $187.60   $187.60  
  Purchase #7 $59.26   8.858%   $64.5093   $64.51   $64.50   $64.50  
  7 purchase totals = $942.45       $1,012.6486   $1,012.65   $1,012.65   $1,012.60