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 $51.71   3.564%   $53.5529   $53.55   $53.55   $53.60  
  Purchase #2 $192.95   9.718%   $211.7009   $211.70   $211.70   $211.70  
  Purchase #3 $159.59   6.159%   $169.4191   $169.42   $169.40   $169.40  
  Purchase #4 $16.74   4.561%   $17.5035   $17.50   $17.50   $17.50  
  Purchase #5 $247.77   9.391%   $271.0381   $271.04   $271.05   $271.00  
  Purchase #6 $50.92   6.345%   $54.1509   $54.15   $54.15   $54.20  
  Purchase #7 $228.50   13.182%   $258.6209   $258.62   $258.60   $258.60  
  7 purchase totals = $948.18       $1,035.9863   $1,035.98   $1,035.95   $1,036.00