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 $193.57   6.401%   $205.9604   $205.96   $205.95   $206.00  
  Purchase #2 $241.95   10.606%   $267.6112   $267.61   $267.60   $267.60  
  Purchase #3 $237.88   9.259%   $259.9053   $259.91   $259.90   $259.90  
  Purchase #4 $22.40   13.181%   $25.3525   $25.35   $25.35   $25.40  
  Purchase #5 $171.56   7.648%   $184.6809   $184.68   $184.70   $184.70  
  Purchase #6 $93.30   4.168%   $97.1887   $97.19   $97.20   $97.20  
  Purchase #7 $32.94   7.283%   $35.339   $35.34   $35.35   $35.30  
  7 purchase totals = $993.60       $1,076.0380   $1,076.04   $1,076.05   $1,076.10