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 $235.39   10.455%   $260   $260.00   $260.00   $260.00  
  Purchase #2 $43.92   5.196%   $46.2021   $46.20   $46.20   $46.20  
  Purchase #3 $203.89   7.151%   $218.4702   $218.47   $218.45   $218.50  
  Purchase #4 $58.57   12.535%   $65.9117   $65.91   $65.90   $65.90  
  Purchase #5 $218.93   8.636%   $237.8368   $237.84   $237.85   $237.80  
  Purchase #6 $167.52   5.634%   $176.9581   $176.96   $176.95   $177.00  
  Purchase #7 $84.93   3.446%   $87.8567   $87.86   $87.85   $87.90  
  7 purchase totals = $1,013.15       $1,093.2356   $1,093.24   $1,093.20   $1,093.30