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 $124.39   7.227%   $133.3797   $133.38   $133.40   $133.40  
  Purchase #2 $247.52   11.543%   $276.0912   $276.09   $276.10   $276.10  
  Purchase #3 $192.49   4.558%   $201.2637   $201.26   $201.25   $201.30  
  Purchase #4 $230.34   9.398%   $251.9874   $251.99   $252.00   $252.00  
  Purchase #5 $16.29   4.313%   $16.9926   $16.99   $17.00   $17.00  
  Purchase #6 $68.43   9.561%   $74.9726   $74.97   $74.95   $75.00  
  Purchase #7 $176.83   11.732%   $197.5757   $197.58   $197.60   $197.60  
  7 purchase totals = $1,056.29       $1,152.2629   $1,152.26   $1,152.30   $1,152.40