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 $235.58   12.493%   $265.011   $265.01   $265.00   $265.00  
  Purchase #2 $75.48   9.620%   $82.7412   $82.74   $82.75   $82.70  
  Purchase #3 $84.79   7.306%   $90.9848   $90.98   $91.00   $91.00  
  Purchase #4 $190.34   11.366%   $211.974   $211.97   $211.95   $212.00  
  Purchase #5 $137.42   13.152%   $155.4935   $155.49   $155.50   $155.50  
  Purchase #6 $125.25   10.802%   $138.7795   $138.78   $138.80   $138.80  
  Purchase #7 $74.32   9.131%   $81.1062   $81.11   $81.10   $81.10  
  7 purchase totals = $923.18       $1,026.0902   $1,026.08   $1,026.10   $1,026.10