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 $161.35   8.381%   $174.8727   $174.87   $174.85   $174.90  
  Purchase #2 $204.77   7.162%   $219.4356   $219.44   $219.45   $219.40  
  Purchase #3 $6.86   8.144%   $7.4187   $7.42   $7.40   $7.40  
  Purchase #4 $74.66   11.592%   $83.3146   $83.31   $83.30   $83.30  
  Purchase #5 $70.90   6.780%   $75.707   $75.71   $75.70   $75.70  
  Purchase #6 $183.36   8.837%   $199.5635   $199.56   $199.55   $199.60  
  Purchase #7 $240.94   9.422%   $263.6414   $263.64   $263.65   $263.60  
  7 purchase totals = $942.84       $1,023.9535   $1,023.95   $1,023.90   $1,023.90