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 $174.85   13.433%   $198.3376   $198.34   $198.35   $198.30  
  Purchase #2 $87.80   7.841%   $94.6844   $94.68   $94.70   $94.70  
  Purchase #3 $182.84   13.506%   $207.5344   $207.53   $207.55   $207.50  
  Purchase #4 $206.33   10.677%   $228.3599   $228.36   $228.35   $228.40  
  Purchase #5 $77.44   7.144%   $82.9723   $82.97   $82.95   $83.00  
  Purchase #6 $40.46   12.652%   $45.579   $45.58   $45.60   $45.60  
  Purchase #7 $196.78   3.103%   $202.8861   $202.89   $202.90   $202.90  
  7 purchase totals = $966.50       $1,060.3537   $1,060.35   $1,060.40   $1,060.40