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 $33.84   11.373%   $37.6886   $37.69   $37.70   $37.70  
  Purchase #2 $79.38   8.297%   $85.9662   $85.97   $85.95   $86.00  
  Purchase #3 $217.81   11.719%   $243.3352   $243.34   $243.35   $243.30  
  Purchase #4 $211.73   9.696%   $232.2593   $232.26   $232.25   $232.30  
  Purchase #5 $158.34   10.700%   $175.2824   $175.28   $175.30   $175.30  
  Purchase #6 $238.82   12.436%   $268.5197   $268.52   $268.50   $268.50  
  Purchase #7 $32.27   6.209%   $34.2736   $34.27   $34.25   $34.30  
  7 purchase totals = $972.19       $1,077.3250   $1,077.33   $1,077.30   $1,077.40