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 $58.60   5.197%   $61.6454   $61.65   $61.65   $61.60  
  Purchase #2 $42.51   7.382%   $45.6481   $45.65   $45.65   $45.60  
  Purchase #3 $17.58   12.550%   $19.7863   $19.79   $19.80   $19.80  
  Purchase #4 $177.43   5.535%   $187.2508   $187.25   $187.25   $187.30  
  Purchase #5 $56.99   3.868%   $59.1944   $59.19   $59.20   $59.20  
  Purchase #6 $193.52   7.319%   $207.6837   $207.68   $207.70   $207.70  
  Purchase #7 $200.93   4.441%   $209.8533   $209.85   $209.85   $209.90  
  7 purchase totals = $747.56       $791.0620   $791.06   $791.10   $791.10