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 $96.52   8.258%   $104.4906   $104.49   $104.50   $104.50  
  Purchase #2 $110.99   12.414%   $124.7683   $124.77   $124.75   $124.80  
  Purchase #3 $65.33   9.661%   $71.6415   $71.64   $71.65   $71.60  
  Purchase #4 $140.43   10.633%   $155.3619   $155.36   $155.35   $155.40  
  Purchase #5 $235.57   4.362%   $245.8456   $245.85   $245.85   $245.80  
  Purchase #6 $75.28   7.583%   $80.9885   $80.99   $81.00   $81.00  
  Purchase #7 $208.97   8.583%   $226.9059   $226.91   $226.90   $226.90  
  7 purchase totals = $933.09       $1,010.0023   $1,010.01   $1,010.00   $1,010.00