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 $225.93   12.438%   $254.0312   $254.03   $254.05   $254.00  
  Purchase #2 $91.87   13.448%   $104.2247   $104.22   $104.20   $104.20  
  Purchase #3 $40.93   6.428%   $43.561   $43.56   $43.55   $43.60  
  Purchase #4 $233.81   5.795%   $247.3593   $247.36   $247.35   $247.40  
  Purchase #5 $95.52   11.740%   $106.734   $106.73   $106.75   $106.70  
  Purchase #6 $137.99   7.441%   $148.2578   $148.26   $148.25   $148.30  
  Purchase #7 $147.86   3.179%   $152.5605   $152.56   $152.55   $152.60  
  7 purchase totals = $973.91       $1,056.7285   $1,056.72   $1,056.70   $1,056.80