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 $45.57   5.140%   $47.9123   $47.91   $47.90   $47.90  
  Purchase #2 $195.83   13.336%   $221.9459   $221.95   $221.95   $221.90  
  Purchase #3 $151.72   5.279%   $159.7293   $159.73   $159.75   $159.70  
  Purchase #4 $241.72   4.819%   $253.3685   $253.37   $253.35   $253.40  
  Purchase #5 $229.94   13.130%   $260.1311   $260.13   $260.15   $260.10  
  Purchase #6 $180.61   4.688%   $189.077   $189.08   $189.10   $189.10  
  Purchase #7 $39.41   4.493%   $41.1807   $41.18   $41.20   $41.20  
  7 purchase totals = $1,084.80       $1,173.3448   $1,173.35   $1,173.40   $1,173.30