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 $53.41   6.371%   $56.8128   $56.81   $56.80   $56.80  
  Purchase #2 $171.83   8.590%   $186.5902   $186.59   $186.60   $186.60  
  Purchase #3 $170.28   4.751%   $178.37   $178.37   $178.35   $178.40  
  Purchase #4 $150.73   10.113%   $165.9733   $165.97   $165.95   $166.00  
  Purchase #5 $162.79   4.168%   $169.5751   $169.58   $169.60   $169.60  
  Purchase #6 $192.89   7.684%   $207.7117   $207.71   $207.70   $207.70  
  Purchase #7 $60.52   6.320%   $64.3449   $64.34   $64.35   $64.30  
  7 purchase totals = $962.45       $1,029.3780   $1,029.37   $1,029.35   $1,029.40