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 $62.87   11.648%   $70.1931   $70.19   $70.20   $70.20  
  Purchase #2 $216.89   11.409%   $241.635   $241.64   $241.65   $241.60  
  Purchase #3 $172.85   11.833%   $193.3033   $193.30   $193.30   $193.30  
  Purchase #4 $185.94   6.707%   $198.411   $198.41   $198.40   $198.40  
  Purchase #5 $33.53   6.785%   $35.805   $35.81   $35.80   $35.80  
  Purchase #6 $108.69   12.320%   $122.0806   $122.08   $122.10   $122.10  
  Purchase #7 $45.51   9.519%   $49.8421   $49.84   $49.85   $49.80  
  7 purchase totals = $826.28       $911.2701   $911.27   $911.30   $911.20