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 $54.69   11.467%   $60.9613   $60.96   $60.95   $61.00  
  Purchase #2 $113.97   3.657%   $118.1379   $118.14   $118.15   $118.10  
  Purchase #3 $141.70   6.247%   $150.552   $150.55   $150.55   $150.60  
  Purchase #4 $79.36   8.535%   $86.1334   $86.13   $86.15   $86.10  
  Purchase #5 $103.49   12.370%   $116.2917   $116.29   $116.30   $116.30  
  Purchase #6 $67.50   12.168%   $75.7134   $75.71   $75.70   $75.70  
  Purchase #7 $24.92   6.440%   $26.5248   $26.52   $26.50   $26.50  
  7 purchase totals = $585.63       $634.3145   $634.30   $634.30   $634.30