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 $135.84   12.433%   $152.729   $152.73   $152.75   $152.70  
  Purchase #2 $203.90   6.345%   $216.8375   $216.84   $216.85   $216.80  
  Purchase #3 $34.76   6.719%   $37.0955   $37.10   $37.10   $37.10  
  Purchase #4 $110.83   12.447%   $124.625   $124.63   $124.65   $124.60  
  Purchase #5 $184.67   7.529%   $198.5738   $198.57   $198.55   $198.60  
  Purchase #6 $140.92   7.281%   $151.1804   $151.18   $151.20   $151.20  
  Purchase #7 $9.64   12.323%   $10.8279   $10.83   $10.85   $10.80  
  7 purchase totals = $820.56       $891.8691   $891.88   $891.95   $891.80