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 $59.61   6.179%   $63.2933   $63.29   $63.30   $63.30  
  Purchase #2 $12.44   4.803%   $13.0375   $13.04   $13.05   $13.00  
  Purchase #3 $135.66   4.524%   $141.7973   $141.80   $141.80   $141.80  
  Purchase #4 $168.85   7.356%   $181.2706   $181.27   $181.25   $181.30  
  Purchase #5 $91.98   6.155%   $97.6414   $97.64   $97.65   $97.60  
  Purchase #6 $147.30   13.657%   $167.4168   $167.42   $167.40   $167.40  
  Purchase #7 $118.36   10.318%   $130.5724   $130.57   $130.55   $130.60  
  7 purchase totals = $734.20       $795.0293   $795.03   $795.00   $795.00