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 $76.87   10.235%   $84.7376   $84.74   $84.75   $84.70  
  Purchase #2 $171.51   5.447%   $180.8521   $180.85   $180.85   $180.90  
  Purchase #3 $200.33   13.596%   $227.5669   $227.57   $227.55   $227.60  
  Purchase #4 $77.66   12.158%   $87.1019   $87.10   $87.10   $87.10  
  Purchase #5 $78.43   13.531%   $89.0424   $89.04   $89.05   $89.00  
  Purchase #6 $148.61   11.517%   $165.7254   $165.73   $165.75   $165.70  
  Purchase #7 $244.65   6.278%   $260.0091   $260.01   $260.00   $260.00  
  7 purchase totals = $998.06       $1,095.0354   $1,095.04   $1,095.05   $1,095.00