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 $50.87   6.110%   $53.9782   $53.98   $54.00   $54.00  
  Purchase #2 $196.27   4.243%   $204.5977   $204.60   $204.60   $204.60  
  Purchase #3 $145.84   4.603%   $152.553   $152.55   $152.55   $152.60  
  Purchase #4 $98.53   3.548%   $102.0258   $102.03   $102.05   $102.00  
  Purchase #5 $250.44   5.392%   $263.9437   $263.94   $263.95   $263.90  
  Purchase #6 $24.26   5.465%   $25.5858   $25.59   $25.60   $25.60  
  Purchase #7 $209.40   13.418%   $237.4973   $237.50   $237.50   $237.50  
  7 purchase totals = $975.61       $1,040.1815   $1,040.19   $1,040.25   $1,040.20