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 $52.64   6.812%   $56.2258   $56.23   $56.25   $56.20  
  Purchase #2 $120.41   3.453%   $124.5678   $124.57   $124.55   $124.60  
  Purchase #3 $23.58   6.398%   $25.0886   $25.09   $25.10   $25.10  
  Purchase #4 $150.41   4.278%   $156.8445   $156.84   $156.85   $156.80  
  Purchase #5 $101.65   4.795%   $106.5241   $106.52   $106.50   $106.50  
  Purchase #6 $104.66   13.285%   $118.5641   $118.56   $118.55   $118.60  
  Purchase #7 $174.97   10.751%   $193.781   $193.78   $193.80   $193.80  
  7 purchase totals = $728.32       $781.5959   $781.59   $781.60   $781.60