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 $96.52   6.869%   $103.15   $103.15   $103.15   $103.20  
  Purchase #2 $210.42   8.796%   $228.9285   $228.93   $228.95   $228.90  
  Purchase #3 $43.32   5.790%   $45.8282   $45.83   $45.85   $45.80  
  Purchase #4 $190.77   11.315%   $212.3556   $212.36   $212.35   $212.40  
  Purchase #5 $49.70   9.509%   $54.426   $54.43   $54.45   $54.40  
  Purchase #6 $120.94   6.268%   $128.5205   $128.52   $128.50   $128.50  
  Purchase #7 $178.31   8.103%   $192.7585   $192.76   $192.75   $192.80  
  7 purchase totals = $889.98       $965.9673   $965.98   $966.00   $966.00