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 $43.26   11.672%   $48.3093   $48.31   $48.30   $48.30  
  Purchase #2 $140.94   6.408%   $149.9714   $149.97   $149.95   $150.00  
  Purchase #3 $73.29   6.584%   $78.1154   $78.12   $78.10   $78.10  
  Purchase #4 $211.59   8.351%   $229.2599   $229.26   $229.25   $229.30  
  Purchase #5 $204.47   12.514%   $230.0574   $230.06   $230.05   $230.10  
  Purchase #6 $30.85   11.812%   $34.494   $34.49   $34.50   $34.50  
  Purchase #7 $142.88   8.182%   $154.5704   $154.57   $154.55   $154.60  
  7 purchase totals = $847.28       $924.7778   $924.78   $924.70   $924.90