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 $54.74   6.110%   $58.0846   $58.08   $58.10   $58.10  
  Purchase #2 $16.69   11.194%   $18.5583   $18.56   $18.55   $18.60  
  Purchase #3 $225.63   12.387%   $253.5788   $253.58   $253.60   $253.60  
  Purchase #4 $247.53   8.170%   $267.7532   $267.75   $267.75   $267.80  
  Purchase #5 $190.87   7.470%   $205.128   $205.13   $205.15   $205.10  
  Purchase #6 $157.74   7.213%   $169.1178   $169.12   $169.10   $169.10  
  Purchase #7 $33.32   10.269%   $36.7416   $36.74   $36.75   $36.70  
  7 purchase totals = $926.52       $1,008.9623   $1,008.96   $1,009.00   $1,009.00