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 $181.81   10.556%   $201.0019   $201.00   $201.00   $201.00  
  Purchase #2 $133.52   12.743%   $150.5345   $150.53   $150.55   $150.50  
  Purchase #3 $50.76   8.152%   $54.898   $54.90   $54.90   $54.90  
  Purchase #4 $221.89   13.771%   $252.4465   $252.45   $252.45   $252.40  
  Purchase #5 $120.92   11.825%   $135.2188   $135.22   $135.20   $135.20  
  Purchase #6 $245.40   6.162%   $260.5215   $260.52   $260.50   $260.50  
  Purchase #7 $103.98   9.742%   $114.1097   $114.11   $114.10   $114.10  
  7 purchase totals = $1,058.28       $1,168.7309   $1,168.73   $1,168.70   $1,168.60