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 $22.30   9.113%   $24.3322   $24.33   $24.35   $24.30  
  Purchase #2 $129.63   8.136%   $140.1767   $140.18   $140.20   $140.20  
  Purchase #3 $156.86   7.789%   $169.0778   $169.08   $169.10   $169.10  
  Purchase #4 $242.49   12.121%   $271.8822   $271.88   $271.90   $271.90  
  Purchase #5 $237.60   12.446%   $267.1717   $267.17   $267.15   $267.20  
  Purchase #6 $58.67   12.433%   $65.9644   $65.96   $65.95   $66.00  
  Purchase #7 $80.43   8.365%   $87.158   $87.16   $87.15   $87.20  
  7 purchase totals = $927.98       $1,025.7630   $1,025.76   $1,025.80   $1,025.90