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 $165.66   9.626%   $181.6064   $181.61   $181.60   $181.60  
  Purchase #2 $150.59   10.537%   $166.4577   $166.46   $166.45   $166.50  
  Purchase #3 $11.32   12.190%   $12.6999   $12.70   $12.70   $12.70  
  Purchase #4 $195.83   10.457%   $216.3079   $216.31   $216.30   $216.30  
  Purchase #5 $126.44   13.768%   $143.8483   $143.85   $143.85   $143.80  
  Purchase #6 $172.66   6.180%   $183.3304   $183.33   $183.35   $183.30  
  Purchase #7 $144.58   9.265%   $157.9753   $157.98   $158.00   $158.00  
  7 purchase totals = $967.08       $1,062.2259   $1,062.24   $1,062.25   $1,062.20