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 $87.47   6.538%   $93.1888   $93.19   $93.20   $93.20  
  Purchase #2 $248.25   4.530%   $259.4957   $259.50   $259.50   $259.50  
  Purchase #3 $65.52   4.409%   $68.4088   $68.41   $68.40   $68.40  
  Purchase #4 $225.66   3.331%   $233.1767   $233.18   $233.20   $233.20  
  Purchase #5 $33.83   11.125%   $37.5936   $37.59   $37.60   $37.60  
  Purchase #6 $119.51   8.445%   $129.6026   $129.60   $129.60   $129.60  
  Purchase #7 $34.97   13.837%   $39.8088   $39.81   $39.80   $39.80  
  7 purchase totals = $815.21       $861.2750   $861.28   $861.30   $861.30