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 $247.48   10.601%   $273.7154   $273.72   $273.70   $273.70  
  Purchase #2 $61.92   11.440%   $69.0036   $69.00   $69.00   $69.00  
  Purchase #3 $36.43   13.289%   $41.2712   $41.27   $41.25   $41.30  
  Purchase #4 $246.96   4.184%   $257.2928   $257.29   $257.30   $257.30  
  Purchase #5 $143.54   11.647%   $160.2581   $160.26   $160.25   $160.30  
  Purchase #6 $60.30   9.288%   $65.9007   $65.90   $65.90   $65.90  
  Purchase #7 $45.85   7.162%   $49.1338   $49.13   $49.15   $49.10  
  7 purchase totals = $842.48       $916.5756   $916.57   $916.55   $916.60