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 $238.82   12.587%   $268.8803   $268.88   $268.90   $268.90  
  Purchase #2 $190.98   6.293%   $202.9984   $203.00   $203.00   $203.00  
  Purchase #3 $106.54   12.593%   $119.9566   $119.96   $119.95   $120.00  
  Purchase #4 $199.84   3.601%   $207.0362   $207.04   $207.05   $207.00  
  Purchase #5 $220.64   13.864%   $251.2295   $251.23   $251.25   $251.20  
  Purchase #6 $169.47   9.792%   $186.0645   $186.06   $186.05   $186.10  
  Purchase #7 $26.64   6.151%   $28.2786   $28.28   $28.30   $28.30  
  7 purchase totals = $1,152.93       $1,264.4441   $1,264.45   $1,264.50   $1,264.50