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 $149.28   10.179%   $164.4752   $164.48   $164.50   $164.50  
  Purchase #2 $219.56   10.354%   $242.2932   $242.29   $242.30   $242.30  
  Purchase #3 $36.77   10.205%   $40.5224   $40.52   $40.50   $40.50  
  Purchase #4 $95.25   8.124%   $102.9881   $102.99   $103.00   $103.00  
  Purchase #5 $159.58   8.542%   $173.2113   $173.21   $173.20   $173.20  
  Purchase #6 $223.43   11.355%   $248.8005   $248.80   $248.80   $248.80  
  Purchase #7 $241.91   6.247%   $257.0221   $257.02   $257.00   $257.00  
  7 purchase totals = $1,125.78       $1,229.3128   $1,229.31   $1,229.30   $1,229.30