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 $61.73   7.514%   $66.3684   $66.37   $66.35   $66.40  
  Purchase #2 $160.27   11.469%   $178.6514   $178.65   $178.65   $178.70  
  Purchase #3 $14.88   11.390%   $16.5748   $16.57   $16.55   $16.60  
  Purchase #4 $189.99   12.672%   $214.0655   $214.07   $214.05   $214.10  
  Purchase #5 $247.61   9.272%   $270.5684   $270.57   $270.55   $270.60  
  Purchase #6 $80.33   13.124%   $90.8725   $90.87   $90.85   $90.90  
  Purchase #7 $171.61   4.201%   $178.8193   $178.82   $178.80   $178.80  
  7 purchase totals = $926.42       $1,015.9203   $1,015.92   $1,015.80   $1,016.10