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 $224.97   13.188%   $254.639   $254.64   $254.65   $254.60  
  Purchase #2 $87.93   4.433%   $91.8279   $91.83   $91.85   $91.80  
  Purchase #3 $81.88   7.523%   $88.0398   $88.04   $88.05   $88.00  
  Purchase #4 $88.46   6.102%   $93.8578   $93.86   $93.85   $93.90  
  Purchase #5 $154.46   8.325%   $167.3188   $167.32   $167.30   $167.30  
  Purchase #6 $23.91   8.476%   $25.9366   $25.94   $25.95   $25.90  
  Purchase #7 $50.61   7.729%   $54.5216   $54.52   $54.50   $54.50  
  7 purchase totals = $712.22       $776.1415   $776.15   $776.15   $776.00