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 $54.38   8.117%   $58.794   $58.79   $58.80   $58.80  
  Purchase #2 $228.52   7.311%   $245.2271   $245.23   $245.25   $245.20  
  Purchase #3 $114.96   12.872%   $129.7577   $129.76   $129.75   $129.80  
  Purchase #4 $235.36   8.668%   $255.761   $255.76   $255.75   $255.80  
  Purchase #5 $168.67   10.320%   $186.0767   $186.08   $186.10   $186.10  
  Purchase #6 $8.94   12.786%   $10.0831   $10.08   $10.10   $10.10  
  Purchase #7 $236.93   8.541%   $257.1662   $257.17   $257.15   $257.20  
  7 purchase totals = $1,047.76       $1,142.8658   $1,142.87   $1,142.90   $1,143.00