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 $52.49   8.772%   $57.0944   $57.09   $57.10   $57.10  
  Purchase #2 $154.54   8.577%   $167.7949   $167.79   $167.80   $167.80  
  Purchase #3 $113.88   9.635%   $124.8523   $124.85   $124.85   $124.90  
  Purchase #4 $212.86   12.216%   $238.863   $238.86   $238.85   $238.90  
  Purchase #5 $102.65   4.189%   $106.95   $106.95   $106.95   $107.00  
  Purchase #6 $212.78   5.506%   $224.4957   $224.50   $224.50   $224.50  
  Purchase #7 $123.84   5.659%   $130.8481   $130.85   $130.85   $130.80  
  7 purchase totals = $973.04       $1,050.8984   $1,050.89   $1,050.90   $1,051.00