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 $35.60   5.164%   $37.4384   $37.44   $37.45   $37.40  
  Purchase #2 $107.65   12.151%   $120.7306   $120.73   $120.75   $120.70  
  Purchase #3 $156.52   4.188%   $163.0751   $163.08   $163.10   $163.10  
  Purchase #4 $54.58   11.788%   $61.0139   $61.01   $61.00   $61.00  
  Purchase #5 $192.44   4.796%   $201.6694   $201.67   $201.65   $201.70  
  Purchase #6 $70.37   6.341%   $74.8322   $74.83   $74.85   $74.80  
  Purchase #7 $104.28   11.527%   $116.3004   $116.30   $116.30   $116.30  
  7 purchase totals = $721.44       $775.0600   $775.06   $775.10   $775.00