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 $175.40   6.837%   $187.3921   $187.39   $187.40   $187.40  
  Purchase #2 $8.80   6.835%   $9.4015   $9.40   $9.40   $9.40  
  Purchase #3 $14.86   12.530%   $16.722   $16.72   $16.70   $16.70  
  Purchase #4 $64.54   6.603%   $68.8016   $68.80   $68.80   $68.80  
  Purchase #5 $83.47   11.221%   $92.8362   $92.84   $92.85   $92.80  
  Purchase #6 $89.74   7.637%   $96.5934   $96.59   $96.60   $96.60  
  Purchase #7 $192.36   10.504%   $212.5655   $212.57   $212.55   $212.60  
  7 purchase totals = $629.17       $684.3123   $684.31   $684.30   $684.30