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 $182.85   11.621%   $204.099   $204.10   $204.10   $204.10  
  Purchase #2 $11.74   12.536%   $13.2117   $13.21   $13.20   $13.20  
  Purchase #3 $181.30   3.657%   $187.9301   $187.93   $187.95   $187.90  
  Purchase #4 $242.42   11.371%   $269.9856   $269.99   $270.00   $270.00  
  Purchase #5 $228.33   5.701%   $241.3471   $241.35   $241.35   $241.30  
  Purchase #6 $58.60   4.318%   $61.1303   $61.13   $61.15   $61.10  
  Purchase #7 $89.95   10.286%   $99.2023   $99.20   $99.20   $99.20  
  7 purchase totals = $995.19       $1,076.9061   $1,076.91   $1,076.95   $1,076.80