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 $182.43   11.757%   $203.8783   $203.88   $203.90   $203.90  
  Purchase #2 $95.94   5.708%   $101.4163   $101.42   $101.40   $101.40  
  Purchase #3 $111.56   13.169%   $126.2513   $126.25   $126.25   $126.30  
  Purchase #4 $219.91   6.333%   $233.8369   $233.84   $233.85   $233.80  
  Purchase #5 $120.95   8.220%   $130.8921   $130.89   $130.90   $130.90  
  Purchase #6 $44.35   3.737%   $46.0074   $46.01   $46.00   $46.00  
  Purchase #7 $138.97   9.433%   $152.079   $152.08   $152.10   $152.10  
  7 purchase totals = $914.11       $994.3613   $994.37   $994.40   $994.40