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 $120.41   6.114%   $127.7719   $127.77   $127.75   $127.80  
  Purchase #2 $183.57   4.283%   $191.4323   $191.43   $191.45   $191.40  
  Purchase #3 $231.53   9.683%   $253.949   $253.95   $253.95   $253.90  
  Purchase #4 $137.38   7.321%   $147.4376   $147.44   $147.45   $147.40  
  Purchase #5 $243.30   11.377%   $270.9802   $270.98   $271.00   $271.00  
  Purchase #6 $193.30   5.771%   $204.4553   $204.46   $204.45   $204.50  
  Purchase #7 $163.96   9.414%   $179.3952   $179.40   $179.40   $179.40  
  7 purchase totals = $1,273.45       $1,375.4215   $1,375.43   $1,375.45   $1,375.40