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 $35.78   5.874%   $37.8817   $37.88   $37.90   $37.90  
  Purchase #2 $247.81   11.122%   $275.3714   $275.37   $275.35   $275.40  
  Purchase #3 $140.54   11.199%   $156.2791   $156.28   $156.30   $156.30  
  Purchase #4 $87.53   9.115%   $95.5084   $95.51   $95.50   $95.50  
  Purchase #5 $118.54   3.561%   $122.7612   $122.76   $122.75   $122.80  
  Purchase #6 $178.43   11.419%   $198.8049   $198.80   $198.80   $198.80  
  Purchase #7 $145.53   12.666%   $163.9628   $163.96   $163.95   $164.00  
  7 purchase totals = $954.16       $1,050.5695   $1,050.56   $1,050.55   $1,050.70