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 $54.85   12.861%   $61.9043   $61.90   $61.90   $61.90  
  Purchase #2 $208.64   8.637%   $226.6602   $226.66   $226.65   $226.70  
  Purchase #3 $95.26   5.211%   $100.224   $100.22   $100.20   $100.20  
  Purchase #4 $80.96   3.229%   $83.5742   $83.57   $83.55   $83.60  
  Purchase #5 $220.82   8.746%   $240.1329   $240.13   $240.15   $240.10  
  Purchase #6 $31.65   9.707%   $34.7223   $34.72   $34.70   $34.70  
  Purchase #7 $181.40   12.872%   $204.7498   $204.75   $204.75   $204.70  
  7 purchase totals = $873.58       $951.9677   $951.95   $951.90   $951.90