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 $226.89   8.428%   $246.0123   $246.01   $246.00   $246.00  
  Purchase #2 $82.46   3.470%   $85.3214   $85.32   $85.30   $85.30  
  Purchase #3 $165.75   6.803%   $177.026   $177.03   $177.05   $177.00  
  Purchase #4 $155.73   9.594%   $170.6707   $170.67   $170.65   $170.70  
  Purchase #5 $43.37   7.121%   $46.4584   $46.46   $46.45   $46.50  
  Purchase #6 $229.46   9.748%   $251.8278   $251.83   $251.85   $251.80  
  Purchase #7 $248.58   6.237%   $264.0839   $264.08   $264.10   $264.10  
  7 purchase totals = $1,152.24       $1,241.4005   $1,241.40   $1,241.40   $1,241.40