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 $180.88   8.191%   $195.6959   $195.70   $195.70   $195.70  
  Purchase #2 $186.47   13.712%   $212.0388   $212.04   $212.05   $212.00  
  Purchase #3 $31.49   7.395%   $33.8187   $33.82   $33.80   $33.80  
  Purchase #4 $30.55   9.867%   $33.5644   $33.56   $33.55   $33.60  
  Purchase #5 $183.36   10.634%   $202.8585   $202.86   $202.85   $202.90  
  Purchase #6 $169.99   10.461%   $187.7727   $187.77   $187.75   $187.80  
  Purchase #7 $112.77   6.657%   $120.2771   $120.28   $120.30   $120.30  
  7 purchase totals = $895.51       $986.0261   $986.03   $986.00   $986.10