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 $62.37   9.291%   $68.1648   $68.16   $68.15   $68.20  
  Purchase #2 $90.52   4.243%   $94.3608   $94.36   $94.35   $94.40  
  Purchase #3 $221.92   10.261%   $244.6912   $244.69   $244.70   $244.70  
  Purchase #4 $198.85   12.364%   $223.4358   $223.44   $223.45   $223.40  
  Purchase #5 $188.28   11.869%   $210.627   $210.63   $210.65   $210.60  
  Purchase #6 $228.57   7.367%   $245.4088   $245.41   $245.40   $245.40  
  Purchase #7 $159.50   11.336%   $177.5809   $177.58   $177.60   $177.60  
  7 purchase totals = $1,150.01       $1,264.2693   $1,264.27   $1,264.30   $1,264.30