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 $218.46   7.559%   $234.9734   $234.97   $234.95   $235.00  
  Purchase #2 $8.57   13.654%   $9.7401   $9.74   $9.75   $9.70  
  Purchase #3 $210.72   7.738%   $227.0255   $227.03   $227.05   $227.00  
  Purchase #4 $97.28   9.372%   $106.3971   $106.40   $106.40   $106.40  
  Purchase #5 $232.99   5.829%   $246.571   $246.57   $246.55   $246.60  
  Purchase #6 $139.69   11.529%   $155.7949   $155.79   $155.80   $155.80  
  Purchase #7 $81.28   10.427%   $89.7551   $89.76   $89.75   $89.80  
  7 purchase totals = $988.99       $1,070.2571   $1,070.26   $1,070.25   $1,070.30