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 $153.27   6.819%   $163.7215   $163.72   $163.70   $163.70  
  Purchase #2 $91.67   11.596%   $102.3001   $102.30   $102.30   $102.30  
  Purchase #3 $39.58   12.223%   $44.4179   $44.42   $44.40   $44.40  
  Purchase #4 $178.49   8.526%   $193.7081   $193.71   $193.70   $193.70  
  Purchase #5 $245.97   5.434%   $259.336   $259.34   $259.35   $259.30  
  Purchase #6 $218.90   6.223%   $232.5221   $232.52   $232.50   $232.50  
  Purchase #7 $240.89   4.727%   $252.2769   $252.28   $252.30   $252.30  
  7 purchase totals = $1,168.77       $1,248.2826   $1,248.29   $1,248.25   $1,248.20