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 $212.76   11.526%   $237.2827   $237.28   $237.30   $237.30  
  Purchase #2 $39.58   13.317%   $44.8509   $44.85   $44.85   $44.90  
  Purchase #3 $117.44   7.416%   $126.1494   $126.15   $126.15   $126.10  
  Purchase #4 $44.80   6.404%   $47.669   $47.67   $47.65   $47.70  
  Purchase #5 $172.59   5.270%   $181.6855   $181.69   $181.70   $181.70  
  Purchase #6 $72.80   3.674%   $75.4747   $75.47   $75.45   $75.50  
  Purchase #7 $242.29   6.496%   $258.0292   $258.03   $258.05   $258.00  
  7 purchase totals = $902.26       $971.1414   $971.14   $971.15   $971.20