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 $216.70   13.110%   $245.1094   $245.11   $245.10   $245.10  
  Purchase #2 $183.31   10.421%   $202.4127   $202.41   $202.40   $202.40  
  Purchase #3 $212.80   3.167%   $219.5394   $219.54   $219.55   $219.50  
  Purchase #4 $66.88   12.274%   $75.0889   $75.09   $75.10   $75.10  
  Purchase #5 $148.83   3.249%   $153.6655   $153.67   $153.65   $153.70  
  Purchase #6 $119.65   8.147%   $129.3979   $129.40   $129.40   $129.40  
  Purchase #7 $176.75   5.155%   $185.8615   $185.86   $185.85   $185.90  
  7 purchase totals = $1,124.92       $1,211.0753   $1,211.08   $1,211.05   $1,211.10