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 $65.54   5.604%   $69.2129   $69.21   $69.20   $69.20  
  Purchase #2 $82.96   13.154%   $93.8726   $93.87   $93.85   $93.90  
  Purchase #3 $83.65   4.670%   $87.5565   $87.56   $87.55   $87.60  
  Purchase #4 $205.96   11.470%   $229.5836   $229.58   $229.60   $229.60  
  Purchase #5 $166.75   3.836%   $173.1465   $173.15   $173.15   $173.10  
  Purchase #6 $92.45   9.245%   $100.997   $101.00   $101.00   $101.00  
  Purchase #7 $99.93   6.821%   $106.7462   $106.75   $106.75   $106.70  
  7 purchase totals = $797.24       $861.1153   $861.12   $861.10   $861.10