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 $83.28   6.683%   $88.8456   $88.85   $88.85   $88.80  
  Purchase #2 $45.55   8.721%   $49.5224   $49.52   $49.50   $49.50  
  Purchase #3 $210.79   5.788%   $222.9905   $222.99   $223.00   $223.00  
  Purchase #4 $31.64   8.423%   $34.305   $34.31   $34.30   $34.30  
  Purchase #5 $192.25   10.777%   $212.9688   $212.97   $212.95   $213.00  
  Purchase #6 $241.40   5.151%   $253.8345   $253.83   $253.85   $253.80  
  Purchase #7 $180.57   10.331%   $199.2247   $199.22   $199.20   $199.20  
  7 purchase totals = $985.48       $1,061.6915   $1,061.69   $1,061.65   $1,061.60