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 $189.44   12.322%   $212.7828   $212.78   $212.80   $212.80  
  Purchase #2 $190.96   13.319%   $216.394   $216.39   $216.40   $216.40  
  Purchase #3 $68.43   8.134%   $73.9961   $74.00   $74.00   $74.00  
  Purchase #4 $168.51   8.663%   $183.108   $183.11   $183.10   $183.10  
  Purchase #5 $174.87   13.220%   $197.9878   $197.99   $198.00   $198.00  
  Purchase #6 $166.94   11.827%   $186.684   $186.68   $186.70   $186.70  
  Purchase #7 $247.61   13.704%   $281.5425   $281.54   $281.55   $281.50  
  7 purchase totals = $1,206.76       $1,352.4952   $1,352.49   $1,352.55   $1,352.50