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 $24.48   11.721%   $27.3493   $27.35   $27.35   $27.30  
  Purchase #2 $226.74   7.410%   $243.5414   $243.54   $243.55   $243.50  
  Purchase #3 $87.66   11.601%   $97.8294   $97.83   $97.85   $97.80  
  Purchase #4 $150.35   9.385%   $164.4603   $164.46   $164.45   $164.50  
  Purchase #5 $31.62   5.173%   $33.2557   $33.26   $33.25   $33.30  
  Purchase #6 $222.77   11.283%   $247.9051   $247.91   $247.90   $247.90  
  Purchase #7 $203.70   13.131%   $230.4478   $230.45   $230.45   $230.40  
  7 purchase totals = $947.32       $1,044.7890   $1,044.80   $1,044.80   $1,044.70