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 $7.96   10.195%   $8.7715   $8.77   $8.75   $8.80  
  Purchase #2 $204.38   6.211%   $217.074   $217.07   $217.05   $217.10  
  Purchase #3 $181.72   11.194%   $202.0617   $202.06   $202.05   $202.10  
  Purchase #4 $164.75   4.689%   $172.4751   $172.48   $172.50   $172.50  
  Purchase #5 $100.62   9.844%   $110.525   $110.53   $110.55   $110.50  
  Purchase #6 $107.89   13.458%   $122.4098   $122.41   $122.40   $122.40  
  Purchase #7 $169.82   13.334%   $192.4638   $192.46   $192.45   $192.50  
  7 purchase totals = $937.14       $1,025.7809   $1,025.78   $1,025.75   $1,025.90