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 $200.93   9.619%   $220.2575   $220.26   $220.25   $220.30  
  Purchase #2 $225.82   11.431%   $251.6335   $251.63   $251.65   $251.60  
  Purchase #3 $60.91   6.604%   $64.9325   $64.93   $64.95   $64.90  
  Purchase #4 $135.83   8.603%   $147.5155   $147.52   $147.50   $147.50  
  Purchase #5 $242.60   7.518%   $260.8387   $260.84   $260.85   $260.80  
  Purchase #6 $49.84   3.319%   $51.4942   $51.49   $51.50   $51.50  
  Purchase #7 $96.28   11.789%   $107.6304   $107.63   $107.65   $107.60  
  7 purchase totals = $1,012.21       $1,104.3023   $1,104.30   $1,104.35   $1,104.20