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 $78.69   7.811%   $84.8365   $84.84   $84.85   $84.80  
  Purchase #2 $158.44   4.475%   $165.5302   $165.53   $165.55   $165.50  
  Purchase #3 $229.58   6.113%   $243.6142   $243.61   $243.60   $243.60  
  Purchase #4 $83.40   5.323%   $87.8394   $87.84   $87.85   $87.80  
  Purchase #5 $245.32   12.153%   $275.1337   $275.13   $275.15   $275.10  
  Purchase #6 $236.25   5.355%   $248.9012   $248.90   $248.90   $248.90  
  Purchase #7 $61.97   6.164%   $65.7898   $65.79   $65.80   $65.80  
  7 purchase totals = $1,093.65       $1,171.6450   $1,171.64   $1,171.70   $1,171.50