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 $177.36   10.873%   $196.6444   $196.64   $196.65   $196.60  
  Purchase #2 $96.84   10.118%   $106.6383   $106.64   $106.65   $106.60  
  Purchase #3 $7.45   11.226%   $8.2863   $8.29   $8.30   $8.30  
  Purchase #4 $221.64   12.226%   $248.7377   $248.74   $248.75   $248.70  
  Purchase #5 $23.56   5.774%   $24.9204   $24.92   $24.90   $24.90  
  Purchase #6 $194.59   6.645%   $207.5205   $207.52   $207.50   $207.50  
  Purchase #7 $28.59   8.818%   $31.1111   $31.11   $31.10   $31.10  
  7 purchase totals = $750.03       $823.8587   $823.86   $823.85   $823.70