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 $187.72   6.227%   $199.4093   $199.41   $199.40   $199.40  
  Purchase #2 $142.28   10.820%   $157.6747   $157.67   $157.65   $157.70  
  Purchase #3 $25.57   6.223%   $27.1612   $27.16   $27.15   $27.20  
  Purchase #4 $147.25   5.625%   $155.5328   $155.53   $155.55   $155.50  
  Purchase #5 $174.39   11.130%   $193.7996   $193.80   $193.80   $193.80  
  Purchase #6 $197.74   5.814%   $209.2366   $209.24   $209.25   $209.20  
  Purchase #7 $173.88   12.790%   $196.1193   $196.12   $196.10   $196.10  
  7 purchase totals = $1,048.83       $1,138.9335   $1,138.93   $1,138.90   $1,138.90