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 $52.26   8.783%   $56.85   $56.85   $56.85   $56.90  
  Purchase #2 $17.35   10.103%   $19.1029   $19.10   $19.10   $19.10  
  Purchase #3 $225.82   7.842%   $243.5288   $243.53   $243.55   $243.50  
  Purchase #4 $155.74   6.507%   $165.874   $165.87   $165.85   $165.90  
  Purchase #5 $130.96   7.552%   $140.8501   $140.85   $140.85   $140.90  
  Purchase #6 $230.68   11.640%   $257.5312   $257.53   $257.55   $257.50  
  Purchase #7 $154.40   6.598%   $164.5873   $164.59   $164.60   $164.60  
  7 purchase totals = $967.21       $1,048.3243   $1,048.32   $1,048.35   $1,048.40