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 $57.64   13.342%   $65.3303   $65.33   $65.35   $65.30  
  Purchase #2 $211.45   12.384%   $237.636   $237.64   $237.65   $237.60  
  Purchase #3 $221.64   10.291%   $244.449   $244.45   $244.45   $244.40  
  Purchase #4 $187.44   10.346%   $206.8325   $206.83   $206.85   $206.80  
  Purchase #5 $134.76   9.425%   $147.4611   $147.46   $147.45   $147.50  
  Purchase #6 $58.88   9.637%   $64.5543   $64.55   $64.55   $64.60  
  Purchase #7 $64.45   12.726%   $72.6519   $72.65   $72.65   $72.70  
  7 purchase totals = $936.26       $1,038.9151   $1,038.91   $1,038.95   $1,038.90