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 $152.59   13.395%   $173.0294   $173.03   $173.05   $173.00  
  Purchase #2 $194.73   5.619%   $205.6719   $205.67   $205.65   $205.70  
  Purchase #3 $181.52   5.677%   $191.8249   $191.82   $191.80   $191.80  
  Purchase #4 $196.43   6.233%   $208.6735   $208.67   $208.65   $208.70  
  Purchase #5 $85.39   7.481%   $91.778   $91.78   $91.80   $91.80  
  Purchase #6 $44.98   8.145%   $48.6436   $48.64   $48.65   $48.60  
  Purchase #7 $31.43   6.234%   $33.3893   $33.39   $33.40   $33.40  
  7 purchase totals = $887.07       $953.0106   $953.00   $953.00   $953.00