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 $153.30   11.308%   $170.6352   $170.64   $170.65   $170.60  
  Purchase #2 $225.61   8.507%   $244.8026   $244.80   $244.80   $244.80  
  Purchase #3 $14.49   10.271%   $15.9783   $15.98   $16.00   $16.00  
  Purchase #4 $99.80   12.477%   $112.252   $112.25   $112.25   $112.30  
  Purchase #5 $10.84   4.654%   $11.3445   $11.34   $11.35   $11.30  
  Purchase #6 $130.94   6.746%   $139.7732   $139.77   $139.75   $139.80  
  Purchase #7 $100.96   5.108%   $106.117   $106.12   $106.10   $106.10  
  7 purchase totals = $735.94       $800.9028   $800.90   $800.90   $800.90