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 $44.91   12.634%   $50.5839   $50.58   $50.60   $50.60  
  Purchase #2 $100.52   4.614%   $105.158   $105.16   $105.15   $105.20  
  Purchase #3 $168.66   11.679%   $188.3578   $188.36   $188.35   $188.40  
  Purchase #4 $192.56   6.342%   $204.7722   $204.77   $204.75   $204.80  
  Purchase #5 $216.32   6.799%   $231.0276   $231.03   $231.05   $231.00  
  Purchase #6 $162.76   11.235%   $181.0461   $181.05   $181.05   $181.00  
  Purchase #7 $29.63   13.410%   $33.6034   $33.60   $33.60   $33.60  
  7 purchase totals = $915.36       $994.5490   $994.55   $994.55   $994.60