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 $57.29   6.195%   $60.8391   $60.84   $60.85   $60.80  
  Purchase #2 $115.52   10.502%   $127.6519   $127.65   $127.65   $127.70  
  Purchase #3 $166.62   4.698%   $174.4478   $174.45   $174.45   $174.40  
  Purchase #4 $32.75   5.498%   $34.5506   $34.55   $34.55   $34.60  
  Purchase #5 $105.85   4.606%   $110.7255   $110.73   $110.75   $110.70  
  Purchase #6 $218.95   11.240%   $243.56   $243.56   $243.55   $243.60  
  Purchase #7 $41.83   13.626%   $47.5298   $47.53   $47.55   $47.50  
  7 purchase totals = $738.81       $799.3047   $799.31   $799.35   $799.30