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 $228.33   11.602%   $254.8208   $254.82   $254.80   $254.80  
  Purchase #2 $176.75   10.641%   $195.558   $195.56   $195.55   $195.60  
  Purchase #3 $43.63   12.341%   $49.0144   $49.01   $49.00   $49.00  
  Purchase #4 $137.31   7.126%   $147.0947   $147.09   $147.10   $147.10  
  Purchase #5 $127.74   8.436%   $138.5161   $138.52   $138.50   $138.50  
  Purchase #6 $178.42   10.208%   $196.6331   $196.63   $196.65   $196.60  
  Purchase #7 $246.78   8.203%   $267.0234   $267.02   $267.00   $267.00  
  7 purchase totals = $1,138.96       $1,248.6605   $1,248.65   $1,248.60   $1,248.60