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 $80.93   6.387%   $86.099   $86.10   $86.10   $86.10  
  Purchase #2 $123.93   3.671%   $128.4795   $128.48   $128.50   $128.50  
  Purchase #3 $246.95   3.338%   $255.1932   $255.19   $255.20   $255.20  
  Purchase #4 $209.95   5.214%   $220.8968   $220.90   $220.90   $220.90  
  Purchase #5 $56.56   7.454%   $60.776   $60.78   $60.80   $60.80  
  Purchase #6 $189.25   12.346%   $212.6148   $212.61   $212.60   $212.60  
  Purchase #7 $68.45   12.720%   $77.1568   $77.16   $77.15   $77.20  
  7 purchase totals = $976.02       $1,041.2161   $1,041.22   $1,041.25   $1,041.30