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 $145.68   10.316%   $160.7083   $160.71   $160.70   $160.70  
  Purchase #2 $36.44   10.640%   $40.3172   $40.32   $40.30   $40.30  
  Purchase #3 $12.36   6.138%   $13.1187   $13.12   $13.10   $13.10  
  Purchase #4 $230.53   3.333%   $238.2136   $238.21   $238.20   $238.20  
  Purchase #5 $175.62   6.466%   $186.9756   $186.98   $187.00   $187.00  
  Purchase #6 $169.60   12.536%   $190.8611   $190.86   $190.85   $190.90  
  Purchase #7 $242.60   7.106%   $259.8392   $259.84   $259.85   $259.80  
  7 purchase totals = $1,012.83       $1,090.0337   $1,090.04   $1,090.00   $1,090.00