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 $245.85   8.228%   $266.0785   $266.08   $266.10   $266.10  
  Purchase #2 $166.49   4.831%   $174.5331   $174.53   $174.55   $174.50  
  Purchase #3 $30.85   7.122%   $33.0471   $33.05   $33.05   $33.00  
  Purchase #4 $245.28   4.448%   $256.1901   $256.19   $256.20   $256.20  
  Purchase #5 $174.30   8.729%   $189.5146   $189.51   $189.50   $189.50  
  Purchase #6 $243.47   10.613%   $269.3095   $269.31   $269.30   $269.30  
  Purchase #7 $83.99   4.756%   $87.9846   $87.98   $88.00   $88.00  
  7 purchase totals = $1,190.23       $1,276.6575   $1,276.65   $1,276.70   $1,276.60