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 $71.82   7.860%   $77.4651   $77.47   $77.45   $77.50  
  Purchase #2 $58.59   10.351%   $64.6547   $64.65   $64.65   $64.70  
  Purchase #3 $120.84   3.734%   $125.3522   $125.35   $125.35   $125.40  
  Purchase #4 $148.64   4.411%   $155.1965   $155.20   $155.20   $155.20  
  Purchase #5 $177.47   11.794%   $198.4008   $198.40   $198.40   $198.40  
  Purchase #6 $223.25   12.794%   $251.8126   $251.81   $251.80   $251.80  
  Purchase #7 $140.42   7.408%   $150.8223   $150.82   $150.80   $150.80  
  7 purchase totals = $941.03       $1,023.7042   $1,023.70   $1,023.65   $1,023.80