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 $76.87   11.133%   $85.4279   $85.43   $85.45   $85.40  
  Purchase #2 $238.58   8.419%   $258.6661   $258.67   $258.65   $258.70  
  Purchase #3 $54.27   4.810%   $56.8804   $56.88   $56.90   $56.90  
  Purchase #4 $149.52   4.297%   $155.9449   $155.94   $155.95   $155.90  
  Purchase #5 $148.37   10.299%   $163.6506   $163.65   $163.65   $163.70  
  Purchase #6 $43.36   6.326%   $46.103   $46.10   $46.10   $46.10  
  Purchase #7 $222.43   9.848%   $244.3349   $244.33   $244.35   $244.30  
  7 purchase totals = $933.40       $1,011.0078   $1,011.00   $1,011.05   $1,011.00