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 $222.43   5.787%   $235.302   $235.30   $235.30   $235.30  
  Purchase #2 $39.91   8.597%   $43.3411   $43.34   $43.35   $43.30  
  Purchase #3 $58.33   12.416%   $65.5723   $65.57   $65.55   $65.60  
  Purchase #4 $36.69   3.225%   $37.8733   $37.87   $37.85   $37.90  
  Purchase #5 $248.36   6.482%   $264.4587   $264.46   $264.45   $264.50  
  Purchase #6 $143.60   8.494%   $155.7974   $155.80   $155.80   $155.80  
  Purchase #7 $211.70   9.841%   $232.5334   $232.53   $232.55   $232.50  
  7 purchase totals = $961.02       $1,034.8782   $1,034.87   $1,034.85   $1,034.90