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 $193.54   11.849%   $216.4726   $216.47   $216.45   $216.50  
  Purchase #2 $241.31   7.625%   $259.7099   $259.71   $259.70   $259.70  
  Purchase #3 $77.44   7.821%   $83.4966   $83.50   $83.50   $83.50  
  Purchase #4 $35.26   5.853%   $37.3238   $37.32   $37.30   $37.30  
  Purchase #5 $84.84   11.291%   $94.4193   $94.42   $94.40   $94.40  
  Purchase #6 $52.35   11.395%   $58.3153   $58.32   $58.30   $58.30  
  Purchase #7 $246.52   10.588%   $272.6215   $272.62   $272.60   $272.60  
  7 purchase totals = $931.26       $1,022.3590   $1,022.36   $1,022.25   $1,022.30