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 $241.84   8.361%   $262.0602   $262.06   $262.05   $262.10  
  Purchase #2 $183.99   10.866%   $203.9824   $203.98   $204.00   $204.00  
  Purchase #3 $224.85   8.644%   $244.286   $244.29   $244.30   $244.30  
  Purchase #4 $165.62   6.668%   $176.6635   $176.66   $176.65   $176.70  
  Purchase #5 $218.86   7.746%   $235.8129   $235.81   $235.80   $235.80  
  Purchase #6 $104.52   4.788%   $109.5244   $109.52   $109.50   $109.50  
  Purchase #7 $8.72   4.696%   $9.1295   $9.13   $9.15   $9.10  
  7 purchase totals = $1,148.40       $1,241.4589   $1,241.45   $1,241.45   $1,241.50