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 $88.94   4.861%   $93.2634   $93.26   $93.25   $93.30  
  Purchase #2 $166.49   5.640%   $175.88   $175.88   $175.90   $175.90  
  Purchase #3 $218.28   5.739%   $230.8071   $230.81   $230.80   $230.80  
  Purchase #4 $51.36   6.184%   $54.5361   $54.54   $54.55   $54.50  
  Purchase #5 $99.27   11.410%   $110.5967   $110.60   $110.60   $110.60  
  Purchase #6 $156.75   5.122%   $164.7787   $164.78   $164.80   $164.80  
  Purchase #7 $200.56   9.547%   $219.7075   $219.71   $219.70   $219.70  
  7 purchase totals = $981.65       $1,049.5695   $1,049.58   $1,049.60   $1,049.60