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 $65.85   7.757%   $70.958   $70.96   $70.95   $71.00  
  Purchase #2 $138.99   10.759%   $153.9439   $153.94   $153.95   $153.90  
  Purchase #3 $51.52   12.804%   $58.1166   $58.12   $58.10   $58.10  
  Purchase #4 $208.39   5.503%   $219.8577   $219.86   $219.85   $219.90  
  Purchase #5 $68.75   11.376%   $76.571   $76.57   $76.55   $76.60  
  Purchase #6 $188.27   9.149%   $205.4948   $205.49   $205.50   $205.50  
  Purchase #7 $214.61   9.650%   $235.3199   $235.32   $235.30   $235.30  
  7 purchase totals = $936.38       $1,020.2619   $1,020.26   $1,020.20   $1,020.30