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 $136.93   13.332%   $155.1855   $155.19   $155.20   $155.20  
  Purchase #2 $197.87   3.639%   $205.0705   $205.07   $205.05   $205.10  
  Purchase #3 $21.52   10.232%   $23.7219   $23.72   $23.70   $23.70  
  Purchase #4 $203.68   3.614%   $211.041   $211.04   $211.05   $211.00  
  Purchase #5 $229.83   4.777%   $240.809   $240.81   $240.80   $240.80  
  Purchase #6 $135.85   4.651%   $142.1684   $142.17   $142.15   $142.20  
  Purchase #7 $218.39   12.707%   $246.1408   $246.14   $246.15   $246.10  
  7 purchase totals = $1,144.07       $1,224.1371   $1,224.14   $1,224.10   $1,224.10