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 $46.63   13.140%   $52.7572   $52.76   $52.75   $52.80  
  Purchase #2 $206.96   9.535%   $226.6936   $226.69   $226.70   $226.70  
  Purchase #3 $85.31   3.631%   $88.4076   $88.41   $88.40   $88.40  
  Purchase #4 $114.25   3.785%   $118.5744   $118.57   $118.55   $118.60  
  Purchase #5 $134.96   9.415%   $147.6665   $147.67   $147.65   $147.70  
  Purchase #6 $234.67   4.395%   $244.9837   $244.98   $245.00   $245.00  
  Purchase #7 $50.47   9.477%   $55.253   $55.25   $55.25   $55.30  
  7 purchase totals = $873.25       $934.3360   $934.33   $934.30   $934.50