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 $221.27   7.171%   $237.1373   $237.14   $237.15   $237.10  
  Purchase #2 $121.61   7.543%   $130.783   $130.78   $130.80   $130.80  
  Purchase #3 $14.34   12.347%   $16.1106   $16.11   $16.10   $16.10  
  Purchase #4 $176.28   8.634%   $191.5   $191.50   $191.50   $191.50  
  Purchase #5 $202.56   10.465%   $223.7579   $223.76   $223.75   $223.80  
  Purchase #6 $159.59   10.816%   $176.8513   $176.85   $176.85   $176.90  
  Purchase #7 $134.87   8.121%   $145.8228   $145.82   $145.80   $145.80  
  7 purchase totals = $1,030.52       $1,121.9629   $1,121.96   $1,121.95   $1,122.00