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 $62.81   7.668%   $67.6263   $67.63   $67.65   $67.60  
  Purchase #2 $39.29   6.574%   $41.8729   $41.87   $41.85   $41.90  
  Purchase #3 $75.29   5.227%   $79.2254   $79.23   $79.25   $79.20  
  Purchase #4 $90.74   5.219%   $95.4757   $95.48   $95.50   $95.50  
  Purchase #5 $208.84   11.499%   $232.8545   $232.85   $232.85   $232.90  
  Purchase #6 $166.58   7.137%   $178.4688   $178.47   $178.45   $178.50  
  Purchase #7 $214.62   5.313%   $226.0228   $226.02   $226.00   $226.00  
  7 purchase totals = $858.17       $921.5464   $921.55   $921.55   $921.60