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 $150.68   12.789%   $169.9505   $169.95   $169.95   $170.00  
  Purchase #2 $28.59   13.660%   $32.4954   $32.50   $32.50   $32.50  
  Purchase #3 $241.32   11.737%   $269.6437   $269.64   $269.65   $269.60  
  Purchase #4 $50.82   4.129%   $52.9184   $52.92   $52.90   $52.90  
  Purchase #5 $231.80   5.163%   $243.7678   $243.77   $243.75   $243.80  
  Purchase #6 $34.73   13.254%   $39.3331   $39.33   $39.35   $39.30  
  Purchase #7 $193.66   12.402%   $217.6777   $217.68   $217.70   $217.70  
  7 purchase totals = $931.60       $1,025.7866   $1,025.79   $1,025.80   $1,025.80