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 $216.29   5.199%   $227.5349   $227.53   $227.55   $227.50  
  Purchase #2 $188.49   4.833%   $197.5997   $197.60   $197.60   $197.60  
  Purchase #3 $120.91   3.788%   $125.4901   $125.49   $125.50   $125.50  
  Purchase #4 $24.84   8.443%   $26.9372   $26.94   $26.95   $26.90  
  Purchase #5 $231.88   5.850%   $245.445   $245.45   $245.45   $245.40  
  Purchase #6 $9.45   9.144%   $10.3141   $10.31   $10.30   $10.30  
  Purchase #7 $127.27   11.732%   $142.2013   $142.20   $142.20   $142.20  
  7 purchase totals = $919.13       $975.5223   $975.52   $975.55   $975.40