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 $132.75   6.429%   $141.2845   $141.28   $141.30   $141.30  
  Purchase #2 $174.59   7.305%   $187.3438   $187.34   $187.35   $187.30  
  Purchase #3 $240.52   11.832%   $268.9783   $268.98   $269.00   $269.00  
  Purchase #4 $206.82   6.172%   $219.5849   $219.58   $219.60   $219.60  
  Purchase #5 $56.55   6.118%   $60.0097   $60.01   $60.00   $60.00  
  Purchase #6 $164.55   7.430%   $176.7761   $176.78   $176.80   $176.80  
  Purchase #7 $88.97   10.161%   $98.0102   $98.01   $98.00   $98.00  
  7 purchase totals = $1,064.75       $1,151.9875   $1,151.98   $1,152.05   $1,152.00