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 $204.87   6.172%   $217.5146   $217.51   $217.50   $217.50  
  Purchase #2 $53.97   3.146%   $55.6679   $55.67   $55.65   $55.70  
  Purchase #3 $250.34   13.760%   $284.7868   $284.79   $284.80   $284.80  
  Purchase #4 $137.28   7.165%   $147.1161   $147.12   $147.10   $147.10  
  Purchase #5 $235.86   12.144%   $264.5028   $264.50   $264.50   $264.50  
  Purchase #6 $196.62   4.114%   $204.7089   $204.71   $204.70   $204.70  
  Purchase #7 $122.32   4.756%   $128.1375   $128.14   $128.15   $128.10  
  7 purchase totals = $1,201.26       $1,302.4346   $1,302.44   $1,302.40   $1,302.40