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 $231.69   6.640%   $247.0742   $247.07   $247.05   $247.10  
  Purchase #2 $156.47   12.691%   $176.3276   $176.33   $176.35   $176.30  
  Purchase #3 $166.53   9.513%   $182.372   $182.37   $182.35   $182.40  
  Purchase #4 $111.32   5.467%   $117.4059   $117.41   $117.40   $117.40  
  Purchase #5 $46.83   8.831%   $50.9656   $50.97   $50.95   $51.00  
  Purchase #6 $161.87   5.711%   $171.1144   $171.11   $171.10   $171.10  
  Purchase #7 $62.31   7.571%   $67.0275   $67.03   $67.05   $67.00  
  7 purchase totals = $937.02       $1,012.2872   $1,012.29   $1,012.25   $1,012.30