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 $53.46   4.869%   $56.063   $56.06   $56.05   $56.10  
  Purchase #2 $64.65   6.447%   $68.818   $68.82   $68.80   $68.80  
  Purchase #3 $247.52   8.630%   $268.881   $268.88   $268.90   $268.90  
  Purchase #4 $203.80   4.444%   $212.8569   $212.86   $212.85   $212.90  
  Purchase #5 $246.34   6.524%   $262.4112   $262.41   $262.40   $262.40  
  Purchase #6 $153.85   6.545%   $163.9195   $163.92   $163.90   $163.90  
  Purchase #7 $189.71   3.201%   $195.7826   $195.78   $195.80   $195.80  
  7 purchase totals = $1,159.33       $1,228.7322   $1,228.73   $1,228.70   $1,228.80