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 $216.76   8.610%   $235.423   $235.42   $235.40   $235.40  
  Purchase #2 $147.74   4.308%   $154.1046   $154.10   $154.10   $154.10  
  Purchase #3 $10.38   6.169%   $11.0203   $11.02   $11.00   $11.00  
  Purchase #4 $71.93   4.753%   $75.3488   $75.35   $75.35   $75.30  
  Purchase #5 $165.50   6.110%   $175.6121   $175.61   $175.60   $175.60  
  Purchase #6 $199.70   6.842%   $213.3635   $213.36   $213.35   $213.40  
  Purchase #7 $148.55   3.532%   $153.7968   $153.80   $153.80   $153.80  
  7 purchase totals = $960.56       $1,018.6691   $1,018.66   $1,018.60   $1,018.60