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 $203.83   4.381%   $212.7598   $212.76   $212.75   $212.80  
  Purchase #2 $82.61   11.151%   $91.8218   $91.82   $91.80   $91.80  
  Purchase #3 $241.47   12.229%   $270.9994   $271.00   $271.00   $271.00  
  Purchase #4 $44.28   6.331%   $47.0834   $47.08   $47.10   $47.10  
  Purchase #5 $97.89   5.639%   $103.41   $103.41   $103.40   $103.40  
  Purchase #6 $57.95   11.787%   $64.7806   $64.78   $64.80   $64.80  
  Purchase #7 $248.26   11.179%   $276.013   $276.01   $276.00   $276.00  
  7 purchase totals = $976.29       $1,066.8680   $1,066.86   $1,066.85   $1,066.90