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 $71.84   12.754%   $81.0025   $81.00   $81.00   $81.00  
  Purchase #2 $144.27   6.696%   $153.9303   $153.93   $153.95   $153.90  
  Purchase #3 $175.83   5.805%   $186.0369   $186.04   $186.05   $186.00  
  Purchase #4 $239.72   11.383%   $267.0073   $267.01   $267.00   $267.00  
  Purchase #5 $149.78   11.513%   $167.0242   $167.02   $167.00   $167.00  
  Purchase #6 $121.26   6.734%   $129.4256   $129.43   $129.45   $129.40  
  Purchase #7 $198.79   10.326%   $219.3171   $219.32   $219.30   $219.30  
  7 purchase totals = $1,101.49       $1,203.7439   $1,203.75   $1,203.75   $1,203.60