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 $34.44   5.395%   $36.298   $36.30   $36.30   $36.30  
  Purchase #2 $74.65   11.237%   $83.0384   $83.04   $83.05   $83.00  
  Purchase #3 $212.89   8.311%   $230.5833   $230.58   $230.60   $230.60  
  Purchase #4 $215.33   7.873%   $232.2829   $232.28   $232.30   $232.30  
  Purchase #5 $77.39   8.412%   $83.9   $83.90   $83.90   $83.90  
  Purchase #6 $196.29   12.225%   $220.2865   $220.29   $220.30   $220.30  
  Purchase #7 $179.60   5.515%   $189.5049   $189.50   $189.50   $189.50  
  7 purchase totals = $990.59       $1,075.8940   $1,075.89   $1,075.95   $1,075.90