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 $154.89   13.598%   $175.9519   $175.95   $175.95   $176.00  
  Purchase #2 $225.32   3.507%   $233.222   $233.22   $233.20   $233.20  
  Purchase #3 $212.58   12.355%   $238.8443   $238.84   $238.85   $238.80  
  Purchase #4 $74.99   13.670%   $85.2411   $85.24   $85.25   $85.20  
  Purchase #5 $215.52   11.859%   $241.0785   $241.08   $241.10   $241.10  
  Purchase #6 $241.72   3.578%   $250.3687   $250.37   $250.35   $250.40  
  Purchase #7 $32.96   3.227%   $34.0236   $34.02   $34.00   $34.00  
  7 purchase totals = $1,157.98       $1,258.7301   $1,258.72   $1,258.70   $1,258.70