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 $208.89   10.506%   $230.836   $230.84   $230.85   $230.80  
  Purchase #2 $57.47   13.354%   $65.1445   $65.14   $65.15   $65.10  
  Purchase #3 $182.81   13.655%   $207.7727   $207.77   $207.75   $207.80  
  Purchase #4 $154.65   8.236%   $167.387   $167.39   $167.40   $167.40  
  Purchase #5 $173.77   4.620%   $181.7982   $181.80   $181.80   $181.80  
  Purchase #6 $26.30   9.800%   $28.8774   $28.88   $28.90   $28.90  
  Purchase #7 $129.60   10.842%   $143.6512   $143.65   $143.65   $143.70  
  7 purchase totals = $933.49       $1,025.4670   $1,025.47   $1,025.50   $1,025.50