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 $246.49   11.859%   $275.7212   $275.72   $275.70   $275.70  
  Purchase #2 $193.75   12.850%   $218.6469   $218.65   $218.65   $218.60  
  Purchase #3 $135.96   11.176%   $151.1549   $151.15   $151.15   $151.20  
  Purchase #4 $165.93   6.132%   $176.1048   $176.10   $176.10   $176.10  
  Purchase #5 $55.30   3.455%   $57.2106   $57.21   $57.20   $57.20  
  Purchase #6 $87.81   4.366%   $91.6438   $91.64   $91.65   $91.60  
  Purchase #7 $37.87   4.694%   $39.6476   $39.65   $39.65   $39.60  
  7 purchase totals = $923.11       $1,010.1298   $1,010.12   $1,010.10   $1,010.00