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 $55.36   11.767%   $61.8742   $61.87   $61.85   $61.90  
  Purchase #2 $232.43   7.787%   $250.5293   $250.53   $250.55   $250.50  
  Purchase #3 $33.94   9.729%   $37.242   $37.24   $37.25   $37.20  
  Purchase #4 $74.48   6.660%   $79.4404   $79.44   $79.45   $79.40  
  Purchase #5 $247.84   9.488%   $271.3551   $271.36   $271.35   $271.40  
  Purchase #6 $134.32   10.869%   $148.9192   $148.92   $148.90   $148.90  
  Purchase #7 $56.96   6.400%   $60.6054   $60.61   $60.60   $60.60  
  7 purchase totals = $835.33       $909.9656   $909.97   $909.95   $909.90