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 $207.59   5.372%   $218.7417   $218.74   $218.75   $218.70  
  Purchase #2 $121.39   11.218%   $135.0075   $135.01   $135.00   $135.00  
  Purchase #3 $231.80   9.129%   $252.961   $252.96   $252.95   $253.00  
  Purchase #4 $61.97   9.816%   $68.053   $68.05   $68.05   $68.10  
  Purchase #5 $119.94   4.570%   $125.4213   $125.42   $125.40   $125.40  
  Purchase #6 $232.75   6.240%   $247.2736   $247.27   $247.25   $247.30  
  Purchase #7 $185.92   13.117%   $210.3071   $210.31   $210.30   $210.30  
  7 purchase totals = $1,161.36       $1,257.7652   $1,257.76   $1,257.70   $1,257.80