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 $88.72   9.194%   $96.8769   $96.88   $96.90   $96.90  
  Purchase #2 $80.42   3.171%   $82.9701   $82.97   $82.95   $83.00  
  Purchase #3 $197.84   3.107%   $203.9869   $203.99   $204.00   $204.00  
  Purchase #4 $153.93   3.571%   $159.4268   $159.43   $159.45   $159.40  
  Purchase #5 $222.52   7.541%   $239.3002   $239.30   $239.30   $239.30  
  Purchase #6 $250.54   13.353%   $283.9946   $283.99   $284.00   $284.00  
  Purchase #7 $125.83   12.774%   $141.9035   $141.90   $141.90   $141.90  
  7 purchase totals = $1,119.80       $1,208.4590   $1,208.46   $1,208.50   $1,208.50