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 $232.90   13.614%   $264.607   $264.61   $264.60   $264.60  
  Purchase #2 $109.62   6.718%   $116.9843   $116.98   $117.00   $117.00  
  Purchase #3 $191.71   10.244%   $211.3488   $211.35   $211.35   $211.30  
  Purchase #4 $7.79   9.431%   $8.5247   $8.52   $8.50   $8.50  
  Purchase #5 $217.68   5.232%   $229.069   $229.07   $229.05   $229.10  
  Purchase #6 $193.79   8.674%   $210.5993   $210.60   $210.60   $210.60  
  Purchase #7 $102.81   3.391%   $106.2963   $106.30   $106.30   $106.30  
  7 purchase totals = $1,056.30       $1,147.4294   $1,147.43   $1,147.40   $1,147.40