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 $24.44   9.829%   $26.8422   $26.84   $26.85   $26.80  
  Purchase #2 $203.55   12.336%   $228.6599   $228.66   $228.65   $228.70  
  Purchase #3 $185.25   13.579%   $210.4051   $210.41   $210.40   $210.40  
  Purchase #4 $110.34   4.522%   $115.3296   $115.33   $115.35   $115.30  
  Purchase #5 $43.42   4.513%   $45.3795   $45.38   $45.40   $45.40  
  Purchase #6 $186.68   6.167%   $198.1926   $198.19   $198.20   $198.20  
  Purchase #7 $190.62   5.146%   $200.4293   $200.43   $200.45   $200.40  
  7 purchase totals = $944.30       $1,025.2382   $1,025.24   $1,025.30   $1,025.20