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 $23.50   9.636%   $25.7645   $25.76   $25.75   $25.80  
  Purchase #2 $170.37   8.148%   $184.2517   $184.25   $184.25   $184.30  
  Purchase #3 $201.35   7.714%   $216.8821   $216.88   $216.90   $216.90  
  Purchase #4 $219.32   3.460%   $226.9085   $226.91   $226.90   $226.90  
  Purchase #5 $55.43   5.281%   $58.3573   $58.36   $58.35   $58.40  
  Purchase #6 $152.31   6.140%   $161.6618   $161.66   $161.65   $161.70  
  Purchase #7 $138.57   12.642%   $156.088   $156.09   $156.10   $156.10  
  7 purchase totals = $960.85       $1,029.9139   $1,029.91   $1,029.90   $1,030.10