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 $162.60   13.346%   $184.3006   $184.30   $184.30   $184.30  
  Purchase #2 $139.57   5.532%   $147.291   $147.29   $147.30   $147.30  
  Purchase #3 $8.52   12.766%   $9.6077   $9.61   $9.60   $9.60  
  Purchase #4 $160.65   11.118%   $178.5111   $178.51   $178.50   $178.50  
  Purchase #5 $11.97   6.341%   $12.729   $12.73   $12.75   $12.70  
  Purchase #6 $236.96   4.345%   $247.2559   $247.26   $247.25   $247.30  
  Purchase #7 $250.32   5.576%   $264.2778   $264.28   $264.30   $264.30  
  7 purchase totals = $970.59       $1,043.9731   $1,043.98   $1,044.00   $1,044.00