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 $160.70   9.272%   $175.6001   $175.60   $175.60   $175.60  
  Purchase #2 $216.42   13.829%   $246.3487   $246.35   $246.35   $246.30  
  Purchase #3 $170.44   12.167%   $191.1774   $191.18   $191.20   $191.20  
  Purchase #4 $181.66   3.826%   $188.6103   $188.61   $188.60   $188.60  
  Purchase #5 $154.54   7.206%   $165.6762   $165.68   $165.70   $165.70  
  Purchase #6 $70.98   12.223%   $79.6559   $79.66   $79.65   $79.70  
  Purchase #7 $36.76   4.278%   $38.3326   $38.33   $38.35   $38.30  
  7 purchase totals = $991.50       $1,085.4012   $1,085.41   $1,085.45   $1,085.40