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 $47.69   8.194%   $51.5977   $51.60   $51.60   $51.60  
  Purchase #2 $195.65   4.703%   $204.8514   $204.85   $204.85   $204.90  
  Purchase #3 $118.57   11.717%   $132.4628   $132.46   $132.45   $132.50  
  Purchase #4 $5.58   7.595%   $6.0038   $6.00   $6.00   $6.00  
  Purchase #5 $120.99   9.866%   $132.9269   $132.93   $132.95   $132.90  
  Purchase #6 $124.65   11.343%   $138.789   $138.79   $138.80   $138.80  
  Purchase #7 $207.44   4.293%   $216.3454   $216.35   $216.35   $216.30  
  7 purchase totals = $820.57       $882.9770   $882.98   $883.00   $883.00