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 $188.50   9.635%   $206.662   $206.66   $206.65   $206.70  
  Purchase #2 $62.50   11.197%   $69.4981   $69.50   $69.50   $69.50  
  Purchase #3 $175.78   12.485%   $197.7261   $197.73   $197.75   $197.70  
  Purchase #4 $23.25   5.636%   $24.5604   $24.56   $24.55   $24.60  
  Purchase #5 $34.58   5.611%   $36.5203   $36.52   $36.50   $36.50  
  Purchase #6 $181.75   4.653%   $190.2068   $190.21   $190.20   $190.20  
  Purchase #7 $243.47   13.212%   $275.6373   $275.64   $275.65   $275.60  
  7 purchase totals = $909.83       $1,000.8110   $1,000.82   $1,000.80   $1,000.80