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 $92.46   4.545%   $96.6623   $96.66   $96.65   $96.70  
  Purchase #2 $49.70   5.215%   $52.2919   $52.29   $52.30   $52.30  
  Purchase #3 $203.26   10.113%   $223.8157   $223.82   $223.80   $223.80  
  Purchase #4 $65.92   8.642%   $71.6168   $71.62   $71.60   $71.60  
  Purchase #5 $222.91   12.632%   $251.068   $251.07   $251.05   $251.10  
  Purchase #6 $206.95   13.854%   $235.6209   $235.62   $235.60   $235.60  
  Purchase #7 $221.35   6.167%   $235.0007   $235.00   $235.00   $235.00  
  7 purchase totals = $1,062.55       $1,166.0763   $1,166.08   $1,166.00   $1,166.10