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 $225.33   12.789%   $254.1475   $254.15   $254.15   $254.10  
  Purchase #2 $144.84   5.789%   $153.2248   $153.22   $153.20   $153.20  
  Purchase #3 $168.46   9.779%   $184.9337   $184.93   $184.95   $184.90  
  Purchase #4 $230.52   3.304%   $238.1364   $238.14   $238.15   $238.10  
  Purchase #5 $88.61   8.332%   $95.993   $95.99   $96.00   $96.00  
  Purchase #6 $108.63   3.645%   $112.5896   $112.59   $112.60   $112.60  
  Purchase #7 $207.45   9.222%   $226.581   $226.58   $226.60   $226.60  
  7 purchase totals = $1,173.84       $1,265.6060   $1,265.60   $1,265.65   $1,265.50