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 $67.57   8.356%   $73.2161   $73.22   $73.20   $73.20  
  Purchase #2 $126.92   13.551%   $144.1189   $144.12   $144.10   $144.10  
  Purchase #3 $31.57   10.815%   $34.9843   $34.98   $35.00   $35.00  
  Purchase #4 $212.46   13.173%   $240.4474   $240.45   $240.45   $240.40  
  Purchase #5 $56.81   6.446%   $60.472   $60.47   $60.45   $60.50  
  Purchase #6 $217.41   9.200%   $237.4117   $237.41   $237.40   $237.40  
  Purchase #7 $209.75   8.579%   $227.7445   $227.74   $227.75   $227.70  
  7 purchase totals = $922.49       $1,018.3949   $1,018.39   $1,018.35   $1,018.30