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 $178.50   10.109%   $196.5446   $196.54   $196.55   $196.50  
  Purchase #2 $23.48   11.198%   $26.1093   $26.11   $26.10   $26.10  
  Purchase #3 $174.37   11.682%   $194.7399   $194.74   $194.75   $194.70  
  Purchase #4 $101.39   4.829%   $106.2861   $106.29   $106.30   $106.30  
  Purchase #5 $139.85   3.535%   $144.7937   $144.79   $144.80   $144.80  
  Purchase #6 $33.75   13.229%   $38.2148   $38.21   $38.20   $38.20  
  Purchase #7 $206.52   6.433%   $219.8054   $219.81   $219.80   $219.80  
  7 purchase totals = $857.86       $926.4938   $926.49   $926.50   $926.40