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 $93.77   10.820%   $103.9159   $103.92   $103.90   $103.90  
  Purchase #2 $212.67   11.782%   $237.7268   $237.73   $237.75   $237.70  
  Purchase #3 $207.72   4.791%   $217.6719   $217.67   $217.65   $217.70  
  Purchase #4 $185.33   9.731%   $203.3645   $203.36   $203.35   $203.40  
  Purchase #5 $24.87   4.402%   $25.9648   $25.96   $25.95   $26.00  
  Purchase #6 $31.87   5.236%   $33.5387   $33.54   $33.55   $33.50  
  Purchase #7 $48.86   7.284%   $52.419   $52.42   $52.40   $52.40  
  7 purchase totals = $805.09       $874.6016   $874.60   $874.55   $874.60