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 $218.57   12.574%   $246.053   $246.05   $246.05   $246.10  
  Purchase #2 $117.48   11.562%   $131.063   $131.06   $131.05   $131.10  
  Purchase #3 $142.74   12.760%   $160.9536   $160.95   $160.95   $161.00  
  Purchase #4 $117.31   5.655%   $123.9439   $123.94   $123.95   $123.90  
  Purchase #5 $77.25   4.454%   $80.6907   $80.69   $80.70   $80.70  
  Purchase #6 $117.41   3.232%   $121.2047   $121.20   $121.20   $121.20  
  Purchase #7 $145.95   11.492%   $162.7226   $162.72   $162.70   $162.70  
  7 purchase totals = $936.71       $1,026.6315   $1,026.61   $1,026.60   $1,026.70