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 $199.57   5.585%   $210.716   $210.72   $210.70   $210.70  
  Purchase #2 $193.89   9.706%   $212.709   $212.71   $212.70   $212.70  
  Purchase #3 $191.26   7.623%   $205.8397   $205.84   $205.85   $205.80  
  Purchase #4 $198.31   9.124%   $216.4038   $216.40   $216.40   $216.40  
  Purchase #5 $120.44   8.589%   $130.7846   $130.78   $130.80   $130.80  
  Purchase #6 $32.30   3.697%   $33.4941   $33.49   $33.50   $33.50  
  Purchase #7 $47.95   4.809%   $50.2559   $50.26   $50.25   $50.30  
  7 purchase totals = $983.72       $1,060.2031   $1,060.20   $1,060.20   $1,060.20