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 $225.85   6.708%   $241   $241.00   $241.00   $241.00  
  Purchase #2 $231.36   12.163%   $259.5003   $259.50   $259.50   $259.50  
  Purchase #3 $37.28   5.349%   $39.2741   $39.27   $39.25   $39.30  
  Purchase #4 $99.44   6.667%   $106.0697   $106.07   $106.05   $106.10  
  Purchase #5 $197.94   5.792%   $209.4047   $209.40   $209.40   $209.40  
  Purchase #6 $97.58   6.350%   $103.7763   $103.78   $103.80   $103.80  
  Purchase #7 $204.97   11.717%   $228.9863   $228.99   $229.00   $229.00  
  7 purchase totals = $1,094.42       $1,188.0114   $1,188.01   $1,188.00   $1,188.10