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 $146.60   11.869%   $164   $164.00   $164.00   $164.00  
  Purchase #2 $217.81   6.503%   $231.9742   $231.97   $231.95   $232.00  
  Purchase #3 $80.80   5.304%   $85.0856   $85.09   $85.10   $85.10  
  Purchase #4 $137.98   7.111%   $147.7918   $147.79   $147.80   $147.80  
  Purchase #5 $201.62   11.637%   $225.0825   $225.08   $225.10   $225.10  
  Purchase #6 $248.26   9.773%   $272.5224   $272.52   $272.50   $272.50  
  Purchase #7 $209.35   11.254%   $232.9102   $232.91   $232.90   $232.90  
  7 purchase totals = $1,242.42       $1,359.3667   $1,359.36   $1,359.35   $1,359.40