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 $9.57   12.650%   $10.7806   $10.78   $10.80   $10.80  
  Purchase #2 $169.37   5.400%   $178.516   $178.52   $178.50   $178.50  
  Purchase #3 $132.46   13.330%   $150.1169   $150.12   $150.10   $150.10  
  Purchase #4 $131.32   5.765%   $138.8906   $138.89   $138.90   $138.90  
  Purchase #5 $145.62   8.370%   $157.8084   $157.81   $157.80   $157.80  
  Purchase #6 $202.58   7.444%   $217.6601   $217.66   $217.65   $217.70  
  Purchase #7 $239.55   12.127%   $268.6002   $268.60   $268.60   $268.60  
  7 purchase totals = $1,030.47       $1,122.3728   $1,122.38   $1,122.35   $1,122.40