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 $46.83   4.801%   $49.0783   $49.08   $49.10   $49.10  
  Purchase #2 $192.45   5.530%   $203.0925   $203.09   $203.10   $203.10  
  Purchase #3 $161.51   9.238%   $176.4303   $176.43   $176.45   $176.40  
  Purchase #4 $107.82   13.706%   $122.5978   $122.60   $122.60   $122.60  
  Purchase #5 $182.62   11.594%   $203.793   $203.79   $203.80   $203.80  
  Purchase #6 $104.71   8.410%   $113.5161   $113.52   $113.50   $113.50  
  Purchase #7 $134.50   4.230%   $140.1894   $140.19   $140.20   $140.20  
  7 purchase totals = $930.44       $1,008.6974   $1,008.70   $1,008.75   $1,008.70