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 $227.52   13.424%   $258.0623   $258.06   $258.05   $258.10  
  Purchase #2 $168.94   5.274%   $177.8499   $177.85   $177.85   $177.80  
  Purchase #3 $65.72   3.647%   $68.1168   $68.12   $68.10   $68.10  
  Purchase #4 $55.41   10.486%   $61.2203   $61.22   $61.20   $61.20  
  Purchase #5 $180.29   12.375%   $202.6009   $202.60   $202.60   $202.60  
  Purchase #6 $43.67   5.783%   $46.1954   $46.20   $46.20   $46.20  
  Purchase #7 $205.76   6.147%   $218.4081   $218.41   $218.40   $218.40  
  7 purchase totals = $947.31       $1,032.4537   $1,032.46   $1,032.40   $1,032.40