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 $160.49   7.486%   $172.5043   $172.50   $172.50   $172.50  
  Purchase #2 $33.55   13.328%   $38.0215   $38.02   $38.00   $38.00  
  Purchase #3 $173.70   7.670%   $187.0228   $187.02   $187.00   $187.00  
  Purchase #4 $88.74   6.722%   $94.7051   $94.71   $94.70   $94.70  
  Purchase #5 $96.43   8.790%   $104.9062   $104.91   $104.90   $104.90  
  Purchase #6 $205.26   13.572%   $233.1179   $233.12   $233.10   $233.10  
  Purchase #7 $223.42   10.572%   $247.04   $247.04   $247.05   $247.00  
  7 purchase totals = $981.59       $1,077.3178   $1,077.32   $1,077.25   $1,077.20