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 $39.41   9.217%   $43.0424   $43.04   $43.05   $43.00  
  Purchase #2 $95.35   11.179%   $106.0092   $106.01   $106.00   $106.00  
  Purchase #3 $63.60   6.450%   $67.7022   $67.70   $67.70   $67.70  
  Purchase #4 $179.78   13.403%   $203.8759   $203.88   $203.90   $203.90  
  Purchase #5 $139.65   5.684%   $147.5877   $147.59   $147.60   $147.60  
  Purchase #6 $79.28   12.518%   $89.2043   $89.20   $89.20   $89.20  
  Purchase #7 $200.27   6.312%   $212.911   $212.91   $212.90   $212.90  
  7 purchase totals = $797.34       $870.3327   $870.33   $870.35   $870.30