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 $208.41   7.362%   $223.7531   $223.75   $223.75   $223.80  
  Purchase #2 $8.50   11.194%   $9.4515   $9.45   $9.45   $9.50  
  Purchase #3 $149.78   6.822%   $159.998   $160.00   $160.00   $160.00  
  Purchase #4 $165.54   9.632%   $181.4848   $181.48   $181.50   $181.50  
  Purchase #5 $170.54   6.182%   $181.0828   $181.08   $181.10   $181.10  
  Purchase #6 $210.97   11.103%   $234.394   $234.39   $234.40   $234.40  
  Purchase #7 $65.44   7.664%   $70.4553   $70.46   $70.45   $70.50  
  7 purchase totals = $979.18       $1,060.6195   $1,060.61   $1,060.65   $1,060.80