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 $194.70   8.713%   $211.6642   $211.66   $211.65   $211.70  
  Purchase #2 $152.55   11.659%   $170.3358   $170.34   $170.35   $170.30  
  Purchase #3 $7.31   12.343%   $8.2123   $8.21   $8.20   $8.20  
  Purchase #4 $225.64   3.127%   $232.6958   $232.70   $232.70   $232.70  
  Purchase #5 $217.87   13.104%   $246.4197   $246.42   $246.40   $246.40  
  Purchase #6 $239.70   12.339%   $269.2766   $269.28   $269.30   $269.30  
  Purchase #7 $60.49   8.433%   $65.5911   $65.59   $65.60   $65.60  
  7 purchase totals = $1,098.26       $1,204.1955   $1,204.20   $1,204.20   $1,204.20