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 $47.93   5.177%   $50.4113   $50.41   $50.40   $50.40  
  Purchase #2 $171.39   13.336%   $194.2466   $194.25   $194.25   $194.20  
  Purchase #3 $211.85   6.560%   $225.7474   $225.75   $225.75   $225.70  
  Purchase #4 $249.87   7.121%   $267.6632   $267.66   $267.65   $267.70  
  Purchase #5 $172.78   6.794%   $184.5187   $184.52   $184.50   $184.50  
  Purchase #6 $158.30   11.564%   $176.6058   $176.61   $176.60   $176.60  
  Purchase #7 $83.41   10.637%   $92.2823   $92.28   $92.30   $92.30  
  7 purchase totals = $1,095.53       $1,191.4753   $1,191.48   $1,191.45   $1,191.40