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 $171.52   6.545%   $182.746   $182.75   $182.75   $182.70  
  Purchase #2 $29.32   12.655%   $33.0304   $33.03   $33.05   $33.00  
  Purchase #3 $31.93   8.153%   $34.5333   $34.53   $34.55   $34.50  
  Purchase #4 $73.73   5.503%   $77.7874   $77.79   $77.80   $77.80  
  Purchase #5 $138.96   3.678%   $144.0709   $144.07   $144.05   $144.10  
  Purchase #6 $83.66   9.143%   $91.309   $91.31   $91.30   $91.30  
  Purchase #7 $200.59   5.467%   $211.5563   $211.56   $211.55   $211.60  
  7 purchase totals = $729.71       $775.0333   $775.04   $775.05   $775.00