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 $52.81   5.254%   $55.5846   $55.58   $55.60   $55.60  
  Purchase #2 $210.82   10.732%   $233.4452   $233.45   $233.45   $233.40  
  Purchase #3 $61.77   8.474%   $67.0044   $67.00   $67.00   $67.00  
  Purchase #4 $150.29   10.520%   $166.1005   $166.10   $166.10   $166.10  
  Purchase #5 $74.37   3.807%   $77.2013   $77.20   $77.20   $77.20  
  Purchase #6 $92.60   8.327%   $100.3108   $100.31   $100.30   $100.30  
  Purchase #7 $120.26   8.344%   $130.2945   $130.29   $130.30   $130.30  
  7 purchase totals = $762.92       $829.9413   $829.93   $829.95   $829.90